This book has been compiled to provide a clear and systematic study of both microprocessors and microcontrollers, with emphasis on widely used families such as the Intel 8085 microprocessor and the Intel 8051 microcontroller. The topics are organized to build a strong conceptual foundation starting from basic architecture and functioning, progressing to assembly language programming, and further to peripheral interfacing and system design. The Testbook presented integrates theoretical concepts with practical examples and problems. This approach not only reinforces learning but also prepares the reader for real-world applications and project work. A variety of solved problems, programming exercises, and case studies are included to enhance understanding and support self-study.