  The present review is based on the lectures that the author had been giving
during several years at the Swiss Federal Institute of Technology in Zurich
(ETH Zurich). Being bounded by lecture frames, the selection of the material,
by necessity, is limited and is motivated by the author's research interests.
The paper gives an introduction to the physics of social systems, providing the
main definitions and notions used in the modeling of these systems. The
behavior of social systems is illustrated by several simple typical models. The
present part considers equilibrium systems. Nonequilibrium systems will be
presented in the second part of the lectures. The style of the paper combines
the features of a tutorial and a survey, which, from one side, makes it easy to
read for nonspecialists aiming at grasping the basics of social physics, and
from the other side, describes several rather recent original models containing
new ideas that could be of interest to experienced researchers in the field.
