This book provides a comprehensive guide to developing augmented reality applications. Starting with an introduction to AR concepts, it explores key tools and platforms, emphasizing Unity as a core development tool. Readers will gain hands-on experience creating marker-based and marker-less AR apps using Vuforia, ARKit, and ARCore. The book takes a practical approach, covering the creation of custom components, C# programming for Unity, and building mobile AR apps. Advanced topics include world-scale AR with Niantic Lightship and optimization strategies for AR app performance. Each chapter builds skills progressively, ensuring a thorough understanding of the subject. By the end, readers will have the confidence and skills to design and develop innovative AR applications, understanding the best practices and challenges of AR app development.