This book is an introduction to a complex domain, with references to its advanced parts and ramifications. It is written with minimal prerequisites — basic general topology and little else — and a moderate progression, starting with a very elementary beginning.
A consistent part of the exposition is organised in the form of exercises, with suitable hints and solutions. The book can be used as a textbook for a first course in algebraic topology or for self-study, and also as a reference book for further study.
It is based on a previous version, which has been entirely reviewed, adding several presentations of advanced subjects, and exploring more deeply the interplay of homology and homotopy.