ABSTRACT
The typical lifetime of a new trend in high-energy physics and cosmology is nowadays about 5-10 years. If it has survived for a longer time, the chances are that it will be with us for quite a while. Inflationary theory by now is 20 years old, and it is still very much alive. It is the only theory which explains why our universe is so homogeneous, flat and isotropic, and why its different parts began their expansion simultaneously. It provides a mechanism explaining galaxy formation and solves numerous different problems at the intersection between cosmology and particle physics. It seems to be in a good agreement with observational data and it does not have any competitors. Thus we have some reasons for optimism.
