The projectors are considered as simple but important type of matrices and operators. Their basic theory can be found in many books, among which Hal- mas 177], 178] are of particular significance. The projectors or projections became an active research area in the last two decades due to ideas generated from linear algebra, statistics and various areas of algorithmic mathematics. There has also grown up a great and increasing number of projection meth- ods for different purposes. The aim of this book is to give a unified survey on projectors and projection methods including the most recent...