  With the increasing number of exoplanets discovered, statistical properties
of the population as a whole become unique constraints on planet formation
models provided a link between the description of the detailed processes
playing a role in this formation and the observed population can be
established. Planet population synthesis provides such a link. The approach
allows to study how different physical models of individual processes (e.g.,
proto-planetary disc structure and evolution, planetesimal formation, gas
accretion, migration, etc.) affect the overall properties of the population of
emerging planets. By necessity, planet population synthesis relies on
simplified descriptions of complex processes. These descriptions can be
obtained from more detailed specialised simulations of these processes. The
objective of this chapter is twofold: 1) provide an overview of the physics
entering in the two main approaches to planet population synthesis and 2)
present some of the results achieved as well as illustrate how it can be used
to extract constraints on the models and to help interpret observations.
