  This monograph introduces the basic concepts of the theory of causal fermion
systems, a recent approach to the description of fundamental physics. The
theory yields quantum mechanics, general relativity and quantum field theory as
limiting cases and is therefore a candidate for a unified physical theory. From
the mathematical perspective, causal fermion systems provide a general
framework for describing and analyzing non-smooth geometries and "quantum
geometries." The dynamics is described by a novel variational principle, called
the causal action principle.
  In addition to the basics, the book provides all the necessary mathematical
background and explains how the causal action principle gives rise to the
interactions of the standard model plus gravity on the level of
second-quantized fermionic fields coupled to classical bosonic fields. The
focus is on getting a mathematically sound connection between causal fermion
systems and physical systems in Minkowski space.
  The book is intended for graduate students entering the field, and is
furthermore a valuable reference work for researchers in quantum field theory
and quantum gravity.
