Stars are important. Understanding the formation of stars in galaxies is central to much of modern astrophysics. However, a quantitative prediction of the star formation rate and the initial distribution of stellar masses remains elusive. For several decades it has been thought that the star formation process is primarily controlled by the interplay between gravity and magnetostatic support, modulated by neutral-ion drift. Recently, however, substantial evidence has accumulated suggesting that supersonic turbulence dominates the motion of gas within molecular clouds and is the main factor determining their internal density and velocity structure. In the talk I will give a short review of theories of star formation and outline the new theory relying on support from driven supersonic turbulence. I will discuss shortly some theories of subsonic turbulence and their generalisation for the case of supersonic motions. At the end main results of numerical simulations of the *molecular* cloud dynamics will be presented.