Formal logic, free from the ambiguities of natural languages, is especially suited for use in computing. In turn, model theory, which is concerned with the relationship between mathematical structures and logic, now has a wide range of applications in areas such as computing, philosophy, and linguistics. Model theory's power comes from its usefulness in defining new structures and in classifying existing ones by establishing links between them. This book, suitable for both mathematicians and students from outside the field, provides a clear and readable introduction to the subject. It includes brief historically background for each major topic and consistently points out the motivations for each new development. The proofs are also explained in detail.