UNIX System Programming explains UNIX system APIs(Application programming interface) that will be used by user application program at the user space as an interface to the UNIX Kernel. This book discusses system programming using UNIX system calls quoting examples written both in C and C++ programming languages. The system APIs discussed in this book are related to File management system, Process management system, Inter Process communications, POSIX threads and other miscellaneous topics. Apart from these system APIs, the book also discusses the overview of compilation process while compiling C/C++ source files. Implementation of static and shared memory is explained in a detailed manner in the appendix section. Implementation of UNIX shell commands using UNIX System APIs are explained where ever necessary. Finally this book is written in a very simple language to avoid difficulty in understanding the concepts making it a suitable text book for both beginners and experienced working professionals.