This textbook provides a first introduction to category theory, a powerful framework and tool for understanding mathematical structures. Designed for students with no previous knowledge of the subject, this book offers a gentle approach to mastering its fundamental principles.

Unlike traditional category theory books, which can often be overwhelming for beginners, this book has been carefully crafted to offer a clear and concise introduction to the subject. It covers all the essential topics, including categories, functors, natural transformations, duality, equivalence, (co)limits, and adjunctions. Abundant fully-worked examples guide readers in understanding the core concepts, while complete proofs and instructive exercises reinforce comprehension and promote self-study. The author also provides background material and references, making the book suitable for those with a basic understanding of groups, rings, modules, topological spaces, and set theory.

Based on the author's course at the Vrije Universiteit Brussel, the book is perfectly suited for classroom use in a first introductory course in category theory. Its clear and concise style, coupled with its detailed coverage of key concepts, makes it equally suited for self-study.

Ana Agore is Senior Researcher at the Institute of Mathematics of the Romanian Academy, Romania, and Guest Professor at Vrije Universiteit Brussel, Belgium. Her research covers topics in quantum groups and Hopf algebras, non-associative algebras, group theory and category theory.

1 Categories and Functors.- 2.- Limits and Colimits.- 3 Adjoint Functors.- 4 Solutions to Selected Exercises.