A programming language refers to a set of rules for converting strings or graphical program elements to several types of machine code output. They are used to implement algorithms in computer programming. The description of a programming language is typically divided into two components, which include semantics and syntax, that are normally defined by a formal language. Specification document defines the programming language in certain cases, while some languages have dominant implementation which is treated as reference. Some languages have both, where basic language is defined by a standard and extensions derived from the dominant implementation. Programming language theory is a sub discipline of computer science concerned with the design, implementation, characterization, development, analysis and categorization of programming languages. This book is a valuable compilation of topics, ranging from the basic to the most complex advancements related to the theoretical and practical aspects of programming languages. It is appropriate for students seeking detailed information in this area of computer science as well as for experts.