Abstract
According to the inflationary universe scenario the universe in the very early stages of its evolution was exponentially expanding in the unstable vacuum-like state. At the end of the exponential expansion (inflation) the energy of the unstable vacuum (of a classical scalar field) transforms into the energy ofhQt dense matter, and the subsequent evolution of the universe is described by the usual hot universe theory . Recently it was realised that the exponential expansion during the very early stages of evolution of the universe naturally occurs in a wide class of realistic theories of elementary particles. The inflationary universe scenario makes it possible to obtain a simple solution to many longstanding cosmological problems and leads to a crucial modification of the standard point of view of the large-scale structure of the universe.