diff --git a/src/main/java/org/springframework/data/repository/CrudRepository.java b/src/main/java/org/springframework/data/repository/CrudRepository.java
index 080986f02..b3570d8d3 100644
--- a/src/main/java/org/springframework/data/repository/CrudRepository.java
+++ b/src/main/java/org/springframework/data/repository/CrudRepository.java
@@ -32,16 +32,17 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param entity must not be {@literal null}.
 	 * @return the saved entity; will never be {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@literal entity} is {@literal null}.
 	 */
 	<S extends T> S save(S entity);
 
 	/**
 	 * Saves all given entities.
 	 *
-	 * @param entities must not be {@literal null} nor must it contain {@literal null}
+	 * @param entities must not be {@literal null} nor must it contain {@literal null}.
 	 * @return the saved entities; will never be {@literal null}. The returned {@literal Iterable} will have the same size
 	 *         as the {@literal Iterable} passed as an argument.
-	 * @throws IllegalArgumentException in case the given {@literal Iterable} or one of its contained entities is
+	 * @throws IllegalArgumentException in case the given {@link Iterable entities} or one of its entities is
 	 *           {@literal null}.
 	 */
 	<S extends T> Iterable<S> saveAll(Iterable<S> entities);
@@ -50,8 +51,8 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Retrieves an entity by its id.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @return the entity with the given id or {@literal Optional#empty()} if none found
-	 * @throws IllegalArgumentException if {@code id} is {@literal null}.
+	 * @return the entity with the given id or {@literal Optional#empty()} if none found.
+	 * @throws IllegalArgumentException if {@literal id} is {@literal null}.
 	 */
 	Optional<T> findById(ID id);
 
@@ -60,7 +61,7 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param id must not be {@literal null}.
 	 * @return {@literal true} if an entity with the given id exists, {@literal false} otherwise.
-	 * @throws IllegalArgumentException if {@code id} is {@literal null}.
+	 * @throws IllegalArgumentException if {@literal id} is {@literal null}.
 	 */
 	boolean existsById(ID id);
 
@@ -72,23 +73,23 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	Iterable<T> findAll();
 
 	/**
-	 * Returns all instances of the type with the given IDs.
+	 * Returns all instances of the type {@code T} with the given IDs.
 	 * <p>
-	 * If some or all ids are not found no entities are returned for these IDs.
+	 * If some or all ids are not found, no entities are returned for these IDs.
 	 * <p>
 	 * Note that the order of elements in the result is not guaranteed.
 	 *
 	 * @param ids must not be {@literal null} nor contain any {@literal null} values.
-	 * @return guaranteed to be not {@literal null}. The size will be equal or smaller than that of the argument.
-	 * @throws IllegalArgumentException in case the given {@literal Iterable} or one of its contained entities is
-	 *           {@literal null}.
+	 * @return guaranteed to be not {@literal null}. The size can be equal or less than the number of given
+	 *         {@literal ids}.
+	 * @throws IllegalArgumentException in case the given {@link Iterable ids} or one of its items is {@literal null}.
 	 */
 	Iterable<T> findAllById(Iterable<ID> ids);
 
 	/**
 	 * Returns the number of entities available.
 	 *
-	 * @return the number of entities
+	 * @return the number of entities.
 	 */
 	long count();
 
@@ -96,7 +97,7 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Deletes the entity with the given id.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @throws IllegalArgumentException in case the given {@code id} is {@literal null}
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}
 	 */
 	void deleteById(ID id);
 
@@ -111,9 +112,8 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 	/**
 	 * Deletes the given entities.
 	 *
-	 * @param entities must not be {@literal null}. Must not contain {@literal null} elements
-	 * @throws IllegalArgumentException in case the given {@literal Iterable} or one of its contained entities is
-	 *           {@literal null}.
+	 * @param entities must not be {@literal null}. Must not contain {@literal null} elements.
+	 * @throws IllegalArgumentException in case the given {@literal entities} or one of its entities is {@literal null}.
 	 */
 	void deleteAll(Iterable<? extends T> entities);
 
diff --git a/src/main/java/org/springframework/data/repository/reactive/ReactiveCrudRepository.java b/src/main/java/org/springframework/data/repository/reactive/ReactiveCrudRepository.java
index 24772b567..ad106bd93 100644
--- a/src/main/java/org/springframework/data/repository/reactive/ReactiveCrudRepository.java
+++ b/src/main/java/org/springframework/data/repository/reactive/ReactiveCrudRepository.java
@@ -41,7 +41,7 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param entity must not be {@literal null}.
 	 * @return {@link Mono} emitting the saved entity.
-	 * @throws IllegalArgumentException in case the given {@code entity} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@literal entity} is {@literal null}.
 	 */
 	<S extends T> Mono<S> save(S entity);
 
@@ -50,7 +50,8 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param entities must not be {@literal null}.
 	 * @return {@link Flux} emitting the saved entities.
-	 * @throws IllegalArgumentException in case the given {@link Iterable} {@code entities} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Iterable entities} or one of its entities is
+	 *           {@literal null}.
 	 */
 	<S extends T> Flux<S> saveAll(Iterable<S> entities);
 
@@ -59,7 +60,7 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param entityStream must not be {@literal null}.
 	 * @return {@link Flux} emitting the saved entities.
-	 * @throws IllegalArgumentException in case the given {@code Publisher} {@code entityStream} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Publisher entityStream} is {@literal null}.
 	 */
 	<S extends T> Flux<S> saveAll(Publisher<S> entityStream);
 
@@ -68,7 +69,7 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param id must not be {@literal null}.
 	 * @return {@link Mono} emitting the entity with the given id or {@link Mono#empty()} if none found.
-	 * @throws IllegalArgumentException in case the given {@code id} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}.
 	 */
 	Mono<T> findById(ID id);
 
@@ -77,16 +78,16 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param id must not be {@literal null}. Uses the first emitted element to perform the find-query.
 	 * @return {@link Mono} emitting the entity with the given id or {@link Mono#empty()} if none found.
-	 * @throws IllegalArgumentException in case the given {@link Publisher} {@code id} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Publisher id} is {@literal null}.
 	 */
 	Mono<T> findById(Publisher<ID> id);
 
 	/**
-	 * Returns whether an entity with the id exists.
+	 * Returns whether an entity with the given {@literal id} exists.
 	 *
 	 * @param id must not be {@literal null}.
 	 * @return {@link Mono} emitting {@literal true} if an entity with the given id exists, {@literal false} otherwise.
-	 * @throws IllegalArgumentException in case the given {@code id} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}.
 	 */
 	Mono<Boolean> existsById(ID id);
 
@@ -95,8 +96,8 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 * element to perform the exists-query.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @return {@link Mono} emitting {@literal true} if an entity with the given id exists, {@literal false} otherwise
-	 * @throws IllegalArgumentException in case the given {@link Publisher} {@code id} is {@literal null}.
+	 * @return {@link Mono} emitting {@literal true} if an entity with the given id exists, {@literal false} otherwise.
+	 * @throws IllegalArgumentException in case the given {@link Publisher id} is {@literal null}.
 	 */
 	Mono<Boolean> existsById(Publisher<ID> id);
 
@@ -108,20 +109,29 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	Flux<T> findAll();
 
 	/**
-	 * Returns all instances with the given IDs.
+	 * Returns all instances of the type {@code T} with the given IDs.
+	 * <p>
+	 * If some or all ids are not found, no entities are returned for these IDs.
+	 * <p>
+	 * Note that the order of elements in the result is not guaranteed.
 	 *
-	 * @param ids must not be {@literal null}.
-	 * @return {@link Flux} emitting the found entities.
-	 * @throws IllegalArgumentException in case the given {@link Iterable} {@code ids} is {@literal null}.
+	 * @param ids must not be {@literal null} nor contain any {@literal null} values.
+	 * @return {@link Flux} emitting the found entities. The size can be equal or less than the number of given
+	 *         {@literal ids}.
+	 * @throws IllegalArgumentException in case the given {@link Iterable ids} or one of its items is {@literal null}.
 	 */
 	Flux<T> findAllById(Iterable<ID> ids);
 
 	/**
-	 * Returns all instances of the type with the given IDs supplied by a {@link Publisher}.
+	 * Returns all instances of the type {@code T} with the given IDs supplied by a {@link Publisher}.
+	 * <p>
+	 * If some or all ids are not found, no entities are returned for these IDs.
+	 * <p>
+	 * Note that the order of elements in the result is not guaranteed.
 	 *
 	 * @param idStream must not be {@literal null}.
 	 * @return {@link Flux} emitting the found entities.
-	 * @throws IllegalArgumentException in case the given {@link Publisher} {@code idStream} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Publisher idStream} is {@literal null}.
 	 */
 	Flux<T> findAllById(Publisher<ID> idStream);
 
@@ -137,7 +147,7 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param id must not be {@literal null}.
 	 * @return {@link Mono} signaling when operation has completed.
-	 * @throws IllegalArgumentException in case the given {@code id} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}.
 	 */
 	Mono<Void> deleteById(ID id);
 
@@ -146,7 +156,7 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param id must not be {@literal null}.
 	 * @return {@link Mono} signaling when operation has completed.
-	 * @throws IllegalArgumentException in case the given {@link Publisher} {@code id} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Publisher id} is {@literal null}.
 	 */
 	Mono<Void> deleteById(Publisher<ID> id);
 
@@ -164,7 +174,8 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param entities must not be {@literal null}.
 	 * @return {@link Mono} signaling when operation has completed.
-	 * @throws IllegalArgumentException in case the given {@link Iterable} {@code entities} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Iterable entities} or one of its entities is
+	 *           {@literal null}.
 	 */
 	Mono<Void> deleteAll(Iterable<? extends T> entities);
 
@@ -173,7 +184,7 @@ public interface ReactiveCrudRepository<T, ID> extends Repository<T, ID> {
 	 *
 	 * @param entityStream must not be {@literal null}.
 	 * @return {@link Mono} signaling when operation has completed.
-	 * @throws IllegalArgumentException in case the given {@link Publisher} {@code entityStream} is {@literal null}.
+	 * @throws IllegalArgumentException in case the given {@link Publisher entityStream} is {@literal null}.
 	 */
 	Mono<Void> deleteAll(Publisher<? extends T> entityStream);
 
diff --git a/src/main/java/org/springframework/data/repository/reactive/RxJava2CrudRepository.java b/src/main/java/org/springframework/data/repository/reactive/RxJava2CrudRepository.java
index 948906042..c7e678e9a 100644
--- a/src/main/java/org/springframework/data/repository/reactive/RxJava2CrudRepository.java
+++ b/src/main/java/org/springframework/data/repository/reactive/RxJava2CrudRepository.java
@@ -42,7 +42,8 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * entity instance completely.
 	 *
 	 * @param entity must not be {@literal null}.
-	 * @return the saved entity.
+	 * @return {@link Single} emitting the saved entity.
+	 * @throws IllegalArgumentException in case the given {@literal entity} is {@literal null}.
 	 */
 	<S extends T> Single<S> save(S entity);
 
@@ -50,8 +51,9 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Saves all given entities.
 	 *
 	 * @param entities must not be {@literal null}.
-	 * @return the saved entities.
-	 * @throws IllegalArgumentException in case the given entity is {@literal null}.
+	 * @return {@link Flowable} emitting the saved entities.
+	 * @throws IllegalArgumentException in case the given {@link Iterable entities} or one of its entities is
+	 *           {@literal null}.
 	 */
 	<S extends T> Flowable<S> saveAll(Iterable<S> entities);
 
@@ -59,8 +61,8 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Saves all given entities.
 	 *
 	 * @param entityStream must not be {@literal null}.
-	 * @return the saved entities.
-	 * @throws IllegalArgumentException in case the given {@code Publisher} is {@literal null}.
+	 * @return {@link Flowable} emitting the saved entities.
+	 * @throws IllegalArgumentException in case the given {@link Flowable entityStream} is {@literal null}.
 	 */
 	<S extends T> Flowable<S> saveAll(Flowable<S> entityStream);
 
@@ -68,26 +70,26 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Retrieves an entity by its id.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @return the entity with the given id or {@link Maybe#empty()} if none found.
-	 * @throws IllegalArgumentException if {@code id} is {@literal null}.
+	 * @return {@link Maybe} emitting the entity with the given id or {@link Maybe#empty()} if none found.
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}.
 	 */
 	Maybe<T> findById(ID id);
 
 	/**
 	 * Retrieves an entity by its id supplied by a {@link Single}.
 	 *
-	 * @param id must not be {@literal null}.
-	 * @return the entity with the given id or {@link Maybe#empty()} if none found.
-	 * @throws IllegalArgumentException if {@code id} is {@literal null}.
+	 * @param id must not be {@literal null}. Uses the first emitted element to perform the find-query.
+	 * @return {@link Maybe} emitting the entity with the given id or {@link Maybe#empty()} if none found.
+	 * @throws IllegalArgumentException in case the given {@link Single id} is {@literal null}.
 	 */
 	Maybe<T> findById(Single<ID> id);
 
 	/**
-	 * Returns whether an entity with the given id exists.
+	 * Returns whether an entity with the given {@literal id} exists.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @return {@literal true} if an entity with the given id exists, {@literal false} otherwise.
-	 * @throws IllegalArgumentException if {@code id} is {@literal null}.
+	 * @return {@link Single} emitting {@literal true} if an entity with the given id exists, {@literal false} otherwise.
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}.
 	 */
 	Single<Boolean> existsById(ID id);
 
@@ -95,38 +97,49 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Returns whether an entity with the given id, supplied by a {@link Single}, exists.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @return {@literal true} if an entity with the given id exists, {@literal false} otherwise.
-	 * @throws IllegalArgumentException if {@code id} is {@literal null}
+	 * @return {@link Single} emitting {@literal true} if an entity with the given id exists, {@literal false} otherwise.
+	 * @throws IllegalArgumentException in case the given {@link Single id} is {@literal null}.
 	 */
 	Single<Boolean> existsById(Single<ID> id);
 
 	/**
 	 * Returns all instances of the type.
 	 *
-	 * @return all entities.
+	 * @return {@link Flowable} emitting all entities.
 	 */
 	Flowable<T> findAll();
 
 	/**
-	 * Returns all instances of the type with the given IDs.
+	 * Returns all instances of the type {@code T} with the given IDs.
+	 * <p>
+	 * If some or all ids are not found, no entities are returned for these IDs.
+	 * <p>
+	 * Note that the order of elements in the result is not guaranteed.
 	 *
-	 * @param ids must not be {@literal null}.
-	 * @return the found entities.
+	 * @param ids must not be {@literal null} nor contain any {@literal null} values.
+	 * @return {@link Flowable} emitting the found entities. The size can be equal or less than the number of given
+	 *         {@literal ids}.
+	 * @throws IllegalArgumentException in case the given {@link Iterable ids} or one of its items is {@literal null}.
 	 */
 	Flowable<T> findAllById(Iterable<ID> ids);
 
 	/**
-	 * Returns all instances of the type with the given IDs.
+	 * Returns all instances of the type {@code T} with the given IDs supplied by a {@link Flowable}.
+	 * <p>
+	 * If some or all ids are not found, no entities are returned for these IDs.
+	 * <p>
+	 * Note that the order of elements in the result is not guaranteed.
 	 *
 	 * @param idStream must not be {@literal null}.
-	 * @return the found entities.
+	 * @return {@link Flowable} emitting the found entities.
+	 * @throws IllegalArgumentException in case the given {@link Flowable idStream} is {@literal null}.
 	 */
 	Flowable<T> findAllById(Flowable<ID> idStream);
 
 	/**
 	 * Returns the number of entities available.
 	 *
-	 * @return the number of entities.
+	 * @return {@link Single} emitting the number of entities.
 	 */
 	Single<Long> count();
 
@@ -134,7 +147,8 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Deletes the entity with the given id.
 	 *
 	 * @param id must not be {@literal null}.
-	 * @throws IllegalArgumentException in case the given {@code id} is {@literal null}.
+	 * @return {@link Completable} signaling when operation has completed.
+	 * @throws IllegalArgumentException in case the given {@literal id} is {@literal null}.
 	 */
 	Completable deleteById(ID id);
 
@@ -142,6 +156,7 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Deletes a given entity.
 	 *
 	 * @param entity must not be {@literal null}.
+	 * @return {@link Completable} signaling when operation has completed.
 	 * @throws IllegalArgumentException in case the given entity is {@literal null}.
 	 */
 	Completable delete(T entity);
@@ -150,20 +165,25 @@ public interface RxJava2CrudRepository<T, ID> extends Repository<T, ID> {
 	 * Deletes the given entities.
 	 *
 	 * @param entities must not be {@literal null}.
-	 * @throws IllegalArgumentException in case the given {@link Iterable} is {@literal null}.
+	 * @return {@link Completable} signaling when operation has completed.
+	 * @throws IllegalArgumentException in case the given {@link Iterable entities} or one of its entities is
+	 *           {@literal null}.
 	 */
 	Completable deleteAll(Iterable<? extends T> entities);
 
 	/**
-	 * Deletes the given entities.
+	 * Deletes the given entities supplied by a {@link Flowable}.
 	 *
 	 * @param entityStream must not be {@literal null}.
-	 * @throws IllegalArgumentException in case the given {@link Flowable} is {@literal null}.
+	 * @return {@link Completable} signaling when operation has completed.
+	 * @throws IllegalArgumentException in case the given {@link Flowable entityStream} is {@literal null}.
 	 */
 	Completable deleteAll(Flowable<? extends T> entityStream);
 
 	/**
 	 * Deletes all entities managed by the repository.
+	 *
+	 * @return {@link Completable} signaling when operation has completed.
 	 */
 	Completable deleteAll();
 }