diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/converter/BookConverter.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/converter/BookConverter.java
new file mode 100644
index 0000000..7cd1df9
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/converter/BookConverter.java
@@ -0,0 +1,42 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.converter;
+ 
+import fr.iut_fbleau.but3.dev62.mylibrary.book.BookDTO;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.BookInfo;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.entity.Book;
+ 
+public final class BookConverter {
+ 
+  private BookConverter() {
+  }
+ 
+  public static Book toDomain(BookInfo bookInfo) {
+    return Book.builder()
+        .isbn(bookInfo.isbn())
+        .title(bookInfo.title())
+        .author(bookInfo.author())
+        .publisher(bookInfo.publisher())
+        .publicationDate(bookInfo.publicationDate())
+        .price(bookInfo.price())
+        .stock(bookInfo.initialStock())
+        .categories(bookInfo.categories())
+        .description(bookInfo.description())
+        .language(bookInfo.language())
+        .build();
+  }
+ 
+  public static BookDTO toDTO(Book book) {
+    return BookDTO.builder()
+        .id(book.getId())
+        .isbn(book.getIsbn())
+        .title(book.getTitle())
+        .author(book.getAuthor())
+        .publisher(book.getPublisher())
+        .publicationDate(book.getPublicationDate())
+        .price(book.getPrice())
+        .stock(book.getStock())
+        .categories(book.getCategories())
+        .description(book.getDescription())
+        .language(book.getLanguage())
+        .build();
+  }
+}
\ No newline at end of file
diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java
new file mode 100644
index 0000000..86f306e
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/entity/Book.java
@@ -0,0 +1,30 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.entity;
+ 
+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.util.List;
+import java.util.UUID;
+import lombok.Builder;
+import lombok.Getter;
+ 
+@Builder
+@Getter
+public class Book {
+ 
+  private UUID id;
+  private String isbn;
+  private String title;
+  private String author;
+  private String publisher;
+  private LocalDate publicationDate;
+  private BigDecimal price;
+  private int stock;
+  private List<String> categories;
+  private String description;
+  private String language;
+ 
+  public void setRandomUUID() {
+    this.id = UUID.randomUUID();
+  }
+}
+ 
\ No newline at end of file
diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/exception/BookNotFoundException.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/exception/BookNotFoundException.java
new file mode 100644
index 0000000..5d59c9c
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/exception/BookNotFoundException.java
@@ -0,0 +1,14 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.exception;
+ 
+import java.text.MessageFormat;
+import java.util.UUID;
+ 
+public class BookNotFoundException extends Exception {
+ 
+  public static final String THE_BOOK_WITH_ID_DOES_NOT_EXIST_MESSAGE = "The book with id {0} does not exist";
+ 
+  public BookNotFoundException(UUID uuid) {
+    super(MessageFormat.format(THE_BOOK_WITH_ID_DOES_NOT_EXIST_MESSAGE, uuid));
+  }
+}
+ 
\ No newline at end of file
diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/exception/NotValidBookException.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/exception/NotValidBookException.java
new file mode 100644
index 0000000..aad876f
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/exception/NotValidBookException.java
@@ -0,0 +1,9 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.exception;
+ 
+public class NotValidBookException extends Exception {
+ 
+  public NotValidBookException(String message) {
+    super(message);
+  }
+}
+ 
\ No newline at end of file
diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/repository/BookRepository.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/repository/BookRepository.java
new file mode 100644
index 0000000..fa3e92b
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/repository/BookRepository.java
@@ -0,0 +1,54 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.repository;
+ 
+import fr.iut_fbleau.but3.dev62.mylibrary.book.entity.Book;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+import java.util.UUID;
+import lombok.NoArgsConstructor;
+ 
+@NoArgsConstructor
+public final class BookRepository {
+ 
+  private final List<Book> books = new ArrayList<>();
+ 
+  public List<Book> findAll() {
+    return books;
+  }
+ 
+  public void deleteAll() {
+    books.clear();
+  }
+ 
+  public Book save(Book newBook) {
+    if (newBook.getId() == null) {
+      newBook.setRandomUUID();
+    }
+    Optional<Book> optionalBookWithSameId = this.findById(newBook.getId());
+    optionalBookWithSameId.ifPresent(books::remove);
+    this.books.add(newBook);
+    return newBook;
+  }
+ 
+  public Optional<Book> findById(UUID uuid) {
+    return this.books.stream()
+        .filter(book -> book.getId().equals(uuid))
+        .findFirst();
+  }
+ 
+  public boolean existsById(UUID uuid) {
+    return this.books.stream()
+        .anyMatch(book -> book.getId().equals(uuid));
+  }
+ 
+  public Optional<Book> findByIsbn(String isbn) {
+    return this.books.stream()
+        .filter(book -> book.getIsbn().equals(isbn))
+        .findFirst();
+  }
+ 
+  public void delete(Book book) {
+    this.books.remove(book);
+  }
+}
+ 
\ No newline at end of file
diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/usecase/BookUseCase.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/usecase/BookUseCase.java
new file mode 100644
index 0000000..662b721
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/usecase/BookUseCase.java
@@ -0,0 +1,67 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.usecase;
+ 
+import fr.iut_fbleau.but3.dev62.mylibrary.book.BookDTO;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.BookInfo;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.converter.BookConverter;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.entity.Book;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.exception.BookNotFoundException;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.exception.NotValidBookException;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.repository.BookRepository;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.validator.BookValidator;
+import java.util.Optional;
+import java.util.UUID;
+ 
+public final class BookUseCase {
+ 
+  private final BookRepository bookRepository;
+ 
+  public BookUseCase(BookRepository bookRepository) {
+    this.bookRepository = bookRepository;
+  }
+ 
+  public String registerBook(BookInfo bookInfo) throws NotValidBookException {
+    BookValidator.validate(bookInfo);
+    Book bookToRegister = BookConverter.toDomain(bookInfo);
+    Book registeredBook = bookRepository.save(bookToRegister);
+    return registeredBook.getIsbn();
+  }
+ 
+  public Optional<BookDTO> findBookByIsbn(String isbn) {
+    Optional<Book> optionalBook = bookRepository.findByIsbn(isbn);
+    return optionalBook.map(BookConverter::toDTO);
+  }
+ 
+  public BookDTO updateBook(UUID uuid, BookInfo bookInfo) throws BookNotFoundException, NotValidBookException {
+    BookValidator.validate(bookInfo);
+    Book existingBook = getBookIfNotFoundThrowException(uuid);
+    Book updatedBook = Book.builder()
+        .id(uuid)
+        .isbn(bookInfo.isbn())
+        .title(bookInfo.title())
+        .author(bookInfo.author())
+        .publisher(bookInfo.publisher())
+        .publicationDate(bookInfo.publicationDate())
+        .price(bookInfo.price())
+        .stock(existingBook.getStock())
+        .categories(bookInfo.categories())
+        .description(bookInfo.description())
+        .language(bookInfo.language())
+        .build();
+    Book saved = bookRepository.save(updatedBook);
+    return BookConverter.toDTO(saved);
+  }
+ 
+  public void deleteBook(UUID uuid) throws BookNotFoundException {
+    Book bookToDelete = getBookIfNotFoundThrowException(uuid);
+    bookRepository.delete(bookToDelete);
+  }
+ 
+  private Book getBookIfNotFoundThrowException(UUID uuid) throws BookNotFoundException {
+    Optional<Book> optionalBook = bookRepository.findById(uuid);
+    if (optionalBook.isEmpty()) {
+      throw new BookNotFoundException(uuid);
+    }
+    return optionalBook.get();
+  }
+}
+ 
\ No newline at end of file
diff --git a/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/validator/BookValidator.java b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/validator/BookValidator.java
new file mode 100644
index 0000000..e0cce37
--- /dev/null
+++ b/src/main/java/fr/iut_fbleau/but3/dev62/mylibrary/book/validator/BookValidator.java
@@ -0,0 +1,59 @@
+package fr.iut_fbleau.but3.dev62.mylibrary.book.validator;
+ 
+import fr.iut_fbleau.but3.dev62.mylibrary.book.BookInfo;
+import fr.iut_fbleau.but3.dev62.mylibrary.book.exception.NotValidBookException;
+import java.math.BigDecimal;
+ 
+public final class BookValidator {
+ 
+  public static final String ISBN_IS_NOT_VALID = "ISBN is not valid";
+  public static final String PRICE_MUST_BE_POSITIVE = "Price must be positive";
+  public static final String TITLE_CANNOT_BE_BLANK = "Title cannot be blank";
+  public static final String AUTHOR_CANNOT_BE_BLANK = "Author cannot be blank";
+  public static final String PUBLISHER_CANNOT_BE_BLANK = "Publisher cannot be blank";
+  public static final String ISBN_REGEX = "\\d{13}";
+ 
+  private BookValidator() {
+  }
+ 
+  public static void validate(BookInfo bookInfo) throws NotValidBookException {
+    validateIsbn(bookInfo);
+    validateTitle(bookInfo);
+    validateAuthor(bookInfo);
+    validatePublisher(bookInfo);
+    validatePrice(bookInfo);
+  }
+ 
+  private static void validateIsbn(BookInfo bookInfo) throws NotValidBookException {
+    if (bookInfo.isbn() == null || bookInfo.isbn().isBlank()) {
+      throw new NotValidBookException(ISBN_IS_NOT_VALID);
+    }
+    if (!bookInfo.isbn().matches(ISBN_REGEX)) {
+      throw new NotValidBookException(ISBN_IS_NOT_VALID);
+    }
+  }
+ 
+  private static void validateTitle(BookInfo bookInfo) throws NotValidBookException {
+    if (bookInfo.title() == null || bookInfo.title().isBlank()) {
+      throw new NotValidBookException(TITLE_CANNOT_BE_BLANK);
+    }
+  }
+ 
+  private static void validateAuthor(BookInfo bookInfo) throws NotValidBookException {
+    if (bookInfo.author() == null || bookInfo.author().isBlank()) {
+      throw new NotValidBookException(AUTHOR_CANNOT_BE_BLANK);
+    }
+  }
+ 
+  private static void validatePublisher(BookInfo bookInfo) throws NotValidBookException {
+    if (bookInfo.publisher() == null || bookInfo.publisher().isBlank()) {
+      throw new NotValidBookException(PUBLISHER_CANNOT_BE_BLANK);
+    }
+  }
+ 
+  private static void validatePrice(BookInfo bookInfo) throws NotValidBookException {
+    if (bookInfo.price() == null || bookInfo.price().compareTo(BigDecimal.ZERO) <= 0) {
+      throw new NotValidBookException(PRICE_MUST_BE_POSITIVE);
+    }
+  }
+}
\ No newline at end of file