This book provides a self-contained pedagogical and constructive presentation of quantum field theory. It contains a comprehensive introduction to the fundamental topics of quantum field theory starting from free fields and their quantization, renormalizable interactions, critical phenomena, the standard model of elementary particle physics, lattice field theory, the functional renormalization group equation, non-commutative field theory, topological field configurations, exact solutions of quantum field theory, supersymmetry and the AdS/CFT correspondence. Written for advanced students, the work provides complete material for a two or three semester course and includes numerous exercises, some with detailed solutions. Readers of this text will be well prepared to follow the theoretical developments in the field and undertake research projects as part of an MSc or PhD programme.