Can mathematics develop without mathematicians, since today computers have already taken over part of their work?  Of course not.  Firstly, the development of science is still impossible without human creativity, and secondly, cooperation is very important in mathematics.  The author of this book tried to introduce the reader to the mathematical community from the inside and talk about international congresses at which scientists get to know each other, share experiences, discuss important problems and try to find ways to solve them.  The history of mathematical congresses is a clear illustration of how huge a role collaboration plays in the development of science.