Are you looking for a practical way to strengthen your modern C++ programming skills while learning how to design reliable, maintainable, and high-performance software? C++26 by Design is written for programmers who want to move beyond isolated coding techniques and understand how professional C++ systems are designed, organized, tested, optimized, and maintained. Could you benefit from a clearer understanding of modern language features, object lifetime, ownership, generic programming, compile-time design, concurrency, performance engineering, software architecture, testing, security, and production development? This book explores these areas through structured explanations and practical programming concepts. It covers the foundations of modern C++, advanced templates and compile-time programming, standard-library techniques, concurrent programming, performance optimization, modular architecture, interface design, reliability, testing, security, build systems, deployment, and large-scale software engineering. Whether you are strengthening existing C++ knowledge, working on larger software projects, or preparing to develop more dependable systems, this guide provides a structured reference for improving both your programming techniques and engineering decisions. The emphasis is on understanding why particular design choices matter, how different C++ features work together, and how to apply them when building software intended to remain maintainable as it grows.