  A condensed introduction to the basic concepts of causal perturbation theory
is given. Causal perturbation theory is a mathematically rigorous approach to
renormalization theory, which makes it possible to put the theoretical setup of
perturbative quantum field theory on a sound mathematical basis by avoiding
infinities from the outset. It goes back to a seminal work by Henri Epstein and
Vladimir Jurko Glaser published in 1973, where a specific causality condition
was imposed at every order of perturbation theory in the case of scalar quantum
field theory such that divergent integrals could be avoided in actual
calculations of loop diagrams. In the meantime, the causal approach has been
applied also to a wide range of gauge theories.
