The book gives an introduction to the field with an emphasis on advanced decomposition method in the task of data mining for common tasks and classification in particular. This book presents a complete methodology for the decomposition of classification problems into smaller and more manageable sub-problems are solved by using existing tools. Benefits of the decomposition methodology in data mining include: increased performance (classification accuracy); conceptual simplification of the problem; feasibility improved for large databases; results clearer and more understandable; runtime is reduced by solving smaller problems and by using parallel / distributed computing, and opportunity to use different techniques for each sub-problem.