This volume deals with the theory of finite topological spaces and itsrelationship with the homotopy and simple homotopy theory of polyhedra. The interaction between their intrinsic combinatorial and topologicalstructures makes finite spaces a useful tool for studying problems inTopology, Algebra and Geometry from a new perspective. In particular,the methods developed in this manuscript are used to study Quillen'sconjecture on the poset of p-subgroups of a finite group and theAndrews-Curtis conjecture on the 3-deformability of contractibletwo-dimensional complexes. This self-contained work constitutes the first detailedexposition on the algebraic topology of finite spaces. It is intendedfor topologists and combinatorialists, but it is also recommended foradvanced undergraduate students and graduate students with a modestknowledge of Algebraic Topology.