Centenary of Alexander Friedmann's Prediction of Universe Expansion and the Prospects of Modern Cosmology

In this Editorial to the Special Issue "The Friedmann Cosmology: A Century Later", we consider an outstanding character of Friedmann's prediction of Universe expansion, which laid the foundation of modern cosmology. The list of the main discoveries made in cosmology during the last one hundred years is followed by a formulation of the standard cosmological model. The articles contributing to the Special Issue are considered in relation to this model, and to several alternative theoretical approaches. Special attention is paid to unresolved problems, such as the nature of dark matter and dark energy, Hubble tension and the pre-inflationary stage of the Universe evolution. The conclusion is made that astrophysics and cosmology are on the threshold of new fundamental discoveries.