Software is a set of instructions that tells a computer how to operate. This is different from hardware, which is the actual component that does the real work. A software system is a system of interconnected software components that make up a computer system. Major categories of software systems comprise programming software, application software development, and system software. A few examples of software systems include database management systems, computer reservations systems, embedded systems, content management systems, and operating systems. A computer program refers to a set of instructions written in a programming language that a computer can execute or understand. Source code is the human-readable version of a computer program. Compilers are used to convert source code into machine instructions creating an executable file. This book contains some path-breaking studies on the theories and methods related to computer programs and software systems. It will serve as a reference to a broad spectrum of readers.