This is an introductory course in ergodic theory, providing a comprehensive overlook over the main aspects and applications of this field.

In the broadest sense, ergodic theory is the study of group actions on measure spaces. Its history traces from Poincare's recurrence theorem in celestial mechanics and Boltzman's ergodic hypothesis in statistical physics to its mathematical proliferation in the 1930s through the ergodic theorems of von Neumann, Birkhoff, and Koopman. It has since grown into a hugely important research area with striking applications to other areas of mathematics, especially number theory and combinatorics. This course provides an introduction to the basics of ergodic theory. Among other things, this includes the theory of recurrence, the structure and convergence of ergodic averages, and the notion of entropy. We will motivate the main ideas and results through simple examples. Another focal point lies on the many groundbreaking applications of ergodic theory in number theory.