For the numerical solution of linear systems of equations arising in image reconstruction, in early 70' has been developed a class of iterative methods, based on projections on the hyperplanes associated to the system s equations. In this respect, firstly as a textbook, the book intends to provide a short and efficient introduction into the field of this class of solvers, and secondly as a short research monograph, it describes author s results, in connection with the ones from the appropriate research directions in the book topic. The book wants to provide an easy to use material in the finite dimensional Euclidean context and the theoretical considerations provide the interested reader with ideas for further developments in Master and PhD theses, research projects and journal papers. The book also addresses to a large number of scientists, from various fields of research in which consistent or inconsistent linear systems of equations arise: image processing, numerical solution of integral equations, linear complementarity problems, non convex optimization, and many others.