The Book has been sectionalized into 9 chapters for step-by-step development. Chapter -1 introduce Microprocessor in Computer, Block diagram of Microcomputer etc.. Chapter -2 presents Architect Chapter- 3 discusses Instruction format and timing diagram of Intel 8085 Microprocessor Chapter- 4 and Chapter 5 introduces Instruction sets of Intel 8085 Microprocessor and 8086 Microprocessor respectively. Chapter 6 discusses programming techniques of 8085 and 8086 Microprocessors. Chapter 7 presents Architecture of 8051 Microcontroller. Chapter 8 includes the 8051 Instruction set. Chapter 9 discusses programming of 8051 microcontroller