This book is intended to cover real algebraic varieties emphasizing the author's program to classify them topologically. The first chapter gives an overview of the classification program. The second chapter provides background material for the rest of the book. It covers subjects starting with the elementary properties of real algebraic sets and ending with the recent solution of the nash conjecture. Chapters three and four develop the theory of resolution towers, which are basic topologically defined objects generalizing the notion of manifold and enable us to study singular spaces in an organized way. Chapter five shows how to obtain algebraic sets from resolution towers. Chapter six explains how to put resolution tower structures on real or complex algebraic sets. Chapter seven applies this theory to real algebraic sets of dimensions less than four by giving their complete topological characterization.