AUTHOR: Apostolos Beligiannis ADDRESS: Department of Mathematics, University of the Aegean, 83200 Karlovassi, Samos, Greece. ABSTRACT: Our aim in this paper is to develop a theory of purity and to prove in a unified conceptual way the existence of almost split morphisms, almost split sequences and almost split triangles in Abstract Homotopy Categories, a rather omnipresent class of categories of interest in representation theory. Our main tool for doing this is the classical Brown Representability Theorem. CURRENT STATUS: Preprint. To appear in Algebras and Representation Theory.