The work describes the Outsourcing in theories. Outsourcing is a fundamental process for many organizations in the world and is essential for solutions in business developing. The research contains data on definition of outsourcing, brief history, types and futures. Further, the paper contains a collection of theories from 1990 to 2006 coming from many interesting authors. The main goal of the book is to present and describe recognizable and valuable outsourcing theories. The paper overviews the following theories: Transaction Cost Economics, Relation View, Core Competences, Evolutionary Economics, Incomplete Contracts, Resourced-based view, Agency theory, Knowledge-based view, Neoclassical economic theory, Social exchange theory, Economics of information. As a summary, the overview for theories will be presented.