  Inflationary theory is already 20 years old, and it is impossible to describe
all of its versions and implications in a short talk. I will concentrate on
several subjects which I believe to be most important. First of all, I will
give a brief review of the first versions of inflationary theory, from
Starobinsky model to new inflation. Then I will describe chaotic inflation, the
theory of quantum fluctuations and density perturbations, the theory of eternal
inflation, and recent observational data. In the second part of the talk I will
discuss the recently proposed ekpyrotic scenario and argue that in its present
form it does not provide a viable alternative to inflation.
