The leading role of supersonic turbulence in the fragmentation of molecular clouds has been established through observational surveys and computer simulations. As the statistical properties of this turbulence are unveiled and understood, we are gradually converging toward a statistical description of the star formation process. In this talk I will summarize our current knowledge of molecular cloud turbulence. I will show how the interaction of turbulence with magnetic fields and gravity can be used to explain the origin of the mass distribution and the formation rate of stars.