This book is aimed at providing an introduction to the basic models of computability to the undergraduate students. This book is devoted to Finite Automata and their properties. Pushdown Automata provides a class of models and enables the analysis of context-free languages. Turing Machines have been introduced and the book discusses computability and decidability. A number of problems with solutions have been provided for each chapter. A lot of exercises have been given with hints/answers to most of these tutorial problems.