This textbook on nonperturbative phenomena stemmed from the lecture courses given for Ph.D. students at the Graduate Schools of the Universities of Pisa and Heidelberg, as well as at the Technical University of Lisbon, in 2009-2011. It describes in detail confinement and confining strings in the Georgi-Glashow model in three dimensions, as well as in the Abelian Higgs model in four dimensions. A separate part of the book is devoted to the Schwinger formulae, the world-line instantons, and the fermionic spin factor in the context of the world-line effective action. The book also illustrates some general analogies between quantum field theory and statistical mechanics, and provides an introduction to the Euclidean finite-temperature field theory, the deconfinement phase transitions, the renormalization group, as well as to such subjects as magnetic monopoles, Wilson loops, basics of nonperturbative quantum chromodynamics, anomalies in gauge theories, and instantons in quantum mechanics.