diff --git a/.idea/misc.xml b/.idea/misc.xml
index 07115cdf..9595f6fa 100644
--- a/.idea/misc.xml
+++ b/.idea/misc.xml
@@ -1,5 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="PWA">
+    <option name="wasEnabledAtLeastOnce" value="true" />
+  </component>
   <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="17" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 00000000..35eb1ddf
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/out/production/s16-Challenge/com/librarysystem/main/LibrarySystem.class b/out/production/s16-Challenge/com/librarysystem/main/LibrarySystem.class
new file mode 100644
index 00000000..0cab47a0
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/main/LibrarySystem.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/manager/BookManager.class b/out/production/s16-Challenge/com/librarysystem/manager/BookManager.class
new file mode 100644
index 00000000..5d61b863
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/manager/BookManager.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/manager/UserManager.class b/out/production/s16-Challenge/com/librarysystem/manager/UserManager.class
new file mode 100644
index 00000000..f1551202
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/manager/UserManager.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/Author.class b/out/production/s16-Challenge/com/librarysystem/model/Author.class
new file mode 100644
index 00000000..b5cb214a
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/Author.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/Book.class b/out/production/s16-Challenge/com/librarysystem/model/Book.class
new file mode 100644
index 00000000..2e2c56f5
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/Book.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/Category.class b/out/production/s16-Challenge/com/librarysystem/model/Category.class
new file mode 100644
index 00000000..03be2811
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/Category.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/Invoice.class b/out/production/s16-Challenge/com/librarysystem/model/Invoice.class
new file mode 100644
index 00000000..3928b46c
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/Invoice.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/Library.class b/out/production/s16-Challenge/com/librarysystem/model/Library.class
new file mode 100644
index 00000000..1f5c3cd0
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/Library.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/Loan.class b/out/production/s16-Challenge/com/librarysystem/model/Loan.class
new file mode 100644
index 00000000..1ae5cf21
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/Loan.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/model/User.class b/out/production/s16-Challenge/com/librarysystem/model/User.class
new file mode 100644
index 00000000..4261e984
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/model/User.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/service/ILoanable.class b/out/production/s16-Challenge/com/librarysystem/service/ILoanable.class
new file mode 100644
index 00000000..2f7a3f51
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/service/ILoanable.class differ
diff --git a/out/production/s16-Challenge/com/librarysystem/service/LibraryService.class b/out/production/s16-Challenge/com/librarysystem/service/LibraryService.class
new file mode 100644
index 00000000..4b9506c4
Binary files /dev/null and b/out/production/s16-Challenge/com/librarysystem/service/LibraryService.class differ
diff --git a/src/Main.java b/src/Main.java
deleted file mode 100644
index 3e59c38f..00000000
--- a/src/Main.java
+++ /dev/null
@@ -1,5 +0,0 @@
-public class Main {
-    public static void main(String[] args) {
-        System.out.println("Hello world!");
-    }
-}
\ No newline at end of file
diff --git a/src/com/librarysystem/main/LibrarySystem.java b/src/com/librarysystem/main/LibrarySystem.java
new file mode 100644
index 00000000..8be87e23
--- /dev/null
+++ b/src/com/librarysystem/main/LibrarySystem.java
@@ -0,0 +1,25 @@
+package com.librarysystem.main;
+
+import com.librarysystem.model.*;
+import com.librarysystem.manager.*;
+import com.librarysystem.service.*;
+
+public class LibrarySystem {
+    public static void main(String[] args) {
+        Library library = new Library();
+        BookManager bookManager = new BookManager(library);
+        UserManager userManager = new UserManager(library);
+        LibraryService libraryService = new LibraryService(library);
+
+        Author author = new Author("George Orwell");
+        Category category = new Category("Dystopian");
+        Book book = new Book("1", "1984", author, category);
+        bookManager.addBook(book);
+
+        User user = new User("1", "Alice");
+        userManager.addUser (user);
+
+        libraryService.loanBook(user, book);
+
+    }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/manager/BookManager.java b/src/com/librarysystem/manager/BookManager.java
new file mode 100644
index 00000000..678b35c2
--- /dev/null
+++ b/src/com/librarysystem/manager/BookManager.java
@@ -0,0 +1,16 @@
+package com.librarysystem.manager;
+
+import com.librarysystem.model.Book;
+import com.librarysystem.model.Library;
+
+public class BookManager {
+    private Library library;
+
+    public BookManager(Library library) {
+        this.library = library;
+    }
+
+    public void addBook(Book book) {
+        library.addBook(book);
+    }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/manager/UserManager.java b/src/com/librarysystem/manager/UserManager.java
new file mode 100644
index 00000000..11193169
--- /dev/null
+++ b/src/com/librarysystem/manager/UserManager.java
@@ -0,0 +1,16 @@
+package com.librarysystem.manager;
+
+import com.librarysystem.model.User;
+import com.librarysystem.model.Library;
+
+public class UserManager {
+    private Library library;
+
+    public UserManager(Library library) {
+        this.library = library;
+    }
+
+    public void addUser (User user) {
+        library.addUser (user);
+    }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/Author.java b/src/com/librarysystem/model/Author.java
new file mode 100644
index 00000000..d6157358
--- /dev/null
+++ b/src/com/librarysystem/model/Author.java
@@ -0,0 +1,12 @@
+package com.librarysystem.model;
+
+public class Author {
+    private String name;
+
+    public Author(String name) {
+        this.name = name;
+    }
+
+    // Getters
+    public String getName() { return name; }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/Book.java b/src/com/librarysystem/model/Book.java
new file mode 100644
index 00000000..f32ba921
--- /dev/null
+++ b/src/com/librarysystem/model/Book.java
@@ -0,0 +1,26 @@
+package com.librarysystem.model;
+
+public class Book {
+    private String id;
+    private String title;
+    private Author author;
+    private Category category;
+    private boolean isAvailable;
+
+    public Book(String id, String title, Author author, Category category) {
+        this.id = id;
+        this.title = title;
+        this.author = author;
+        this.category = category;
+        this.isAvailable = true;
+    }
+
+    // Getters and Setters
+    public String getId() { return id; }
+    public String getTitle() { return title; }
+    public Author getAuthor() { return author; }
+    public Category getCategory() { return category; }
+    public boolean isAvailable() { return isAvailable; }
+    public void setAvailable(boolean available) { isAvailable = available; }
+    public void setTitle(String title) { this.title = title; }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/Category.java b/src/com/librarysystem/model/Category.java
new file mode 100644
index 00000000..74903663
--- /dev/null
+++ b/src/com/librarysystem/model/Category.java
@@ -0,0 +1,12 @@
+package com.librarysystem.model;
+
+public class Category {
+    private String name;
+
+    public Category(String name) {
+        this.name = name;
+    }
+
+    // Getters
+    public String getName() { return name; }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/Invoice.java b/src/com/librarysystem/model/Invoice.java
new file mode 100644
index 00000000..3de8e4ab
--- /dev/null
+++ b/src/com/librarysystem/model/Invoice.java
@@ -0,0 +1,16 @@
+package com.librarysystem.model;
+
+public class Invoice {
+    private User user;
+    private Book book;
+    private double amount;
+
+    public Invoice(User user, Book book, double amount) {
+        this.user = user;
+        this.book = book;
+        this.amount = amount;
+    }
+
+    // Getters
+    public double getAmount() { return amount; }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/Library.java b/src/com/librarysystem/model/Library.java
new file mode 100644
index 00000000..8b91a8c5
--- /dev/null
+++ b/src/com/librarysystem/model/Library.java
@@ -0,0 +1,56 @@
+package com.librarysystem.model;
+
+import com.librarysystem.service.ILoanable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Library implements ILoanable {
+    private List<Book> books;
+    private List<User> users;
+    private List<Loan> loans;
+
+    public Library() {
+        this.books = new ArrayList<>();
+        this.users = new ArrayList<>();
+        this.loans = new ArrayList<>();
+    }
+
+    public void addBook(Book book) {
+        books.add(book);
+    }
+
+    public void addUser (User user) {
+        users.add(user);
+    }
+
+    public List<Book> getBooks() {
+        return books;
+    }
+
+    public List<User> getUsers() {
+        return users;
+    }
+
+    @Override
+    public void loanBook(User user, Book book) {
+        if (book.isAvailable()) {
+            book.setAvailable(false);
+            loans.add(new Loan(user, book));
+            System.out.println(user.getName() + " has borrowed " + book.getTitle());
+        } else {
+            System.out.println("The book is not available.");
+        }
+    }
+
+    @Override
+    public void returnBook(User user, Book book) {
+        if (loans.stream().anyMatch(loan -> loan.getUser ().equals(user) && loan.getBook().equals(book))) {
+            book.setAvailable(true);
+            loans.removeIf(loan -> loan.getUser ().equals(user) && loan.getBook().equals(book));
+            System.out.println(user.getName() + " has returned " + book.getTitle());
+        } else {
+            System.out.println("This book was not borrowed by the user.");
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/Loan.java b/src/com/librarysystem/model/Loan.java
new file mode 100644
index 00000000..4515c5f7
--- /dev/null
+++ b/src/com/librarysystem/model/Loan.java
@@ -0,0 +1,20 @@
+package com.librarysystem.model;
+
+import java.util.Date;
+
+public class Loan {
+    private User user;
+    private Book book;
+    private Date loanDate;
+
+    public Loan(User user, Book book) {
+        this.user = user;
+        this.book = book;
+        this.loanDate = new Date();
+    }
+
+    // Getters
+    public User getUser () { return user; }
+    public Book getBook() { return book; }
+    public Date getLoanDate() { return loanDate; }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/model/User.java b/src/com/librarysystem/model/User.java
new file mode 100644
index 00000000..8221f611
--- /dev/null
+++ b/src/com/librarysystem/model/User.java
@@ -0,0 +1,21 @@
+package com.librarysystem.model;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class User {
+    private String id;
+    private String name;
+    private Set<Book> borrowedBooks;
+
+    public User(String id, String name) {
+        this.id = id;
+        this.name = name;
+        this.borrowedBooks = new HashSet<>();
+    }
+
+    // Getters and Setters
+    public String getId() { return id; }
+    public String getName() { return name; }
+    public Set<Book> getBorrowedBooks() { return borrowedBooks; }
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/service/ILoanable.java b/src/com/librarysystem/service/ILoanable.java
new file mode 100644
index 00000000..4d4834f1
--- /dev/null
+++ b/src/com/librarysystem/service/ILoanable.java
@@ -0,0 +1,9 @@
+package com.librarysystem.service;
+
+import com.librarysystem.model.User;
+import com.librarysystem.model.Book;
+
+public interface ILoanable {
+    void loanBook(User user, Book book);
+    void returnBook(User user, Book book);
+}
\ No newline at end of file
diff --git a/src/com/librarysystem/service/LibraryService.java b/src/com/librarysystem/service/LibraryService.java
new file mode 100644
index 00000000..9c62931f
--- /dev/null
+++ b/src/com/librarysystem/service/LibraryService.java
@@ -0,0 +1,21 @@
+package com.librarysystem.service;
+
+import com.librarysystem.model.Library;
+import com.librarysystem.model.User;
+import com.librarysystem.model.Book;
+
+public class LibraryService {
+    private Library library;
+
+    public LibraryService(Library library) {
+        this.library = library;
+    }
+
+    public void loanBook(User user, Book book) {
+        library.loanBook(user, book);
+    }
+
+    public void returnBook(User user, Book book) {
+        library.returnBook(user, book);
+    }
+}
\ No newline at end of file