This book divided in eleven chapters, in the first chapter describes basics of a compiler, its definition and its types. It also includes the need of a compiler. The second chapter deals with phases of compiler, frontend and book end of compiler, single pass and multiphase compiler; Chapter three covers role of logical analyzer, description of tokens, automata, the fourth chapter presents syntax analyzer, grammar, LMD, RMD, passing techniques. Fifth chapter gives syntax directed translation, syntax tree, attributes such as synthesis and inherited. Chapter six deals with type checking, its definition, dynamic type checking and equivalence of it, function overloading and parameter passing. Chapter seven covers run time environment storage allocation techniques, symbol table. Chapter eight presents intermediate code generators, techniques of ICG, conversion. Chapter nine deals with code generation, basic blocks, flow graph, peephole optimization while chapter ten is on code optimization, that contains optimization of basic blocks, reducible flow graph, data flow analysis and global analysis. Chapter eleven one-pass compiler, compiler, its structure, STD rules and passing are described.