Random lasing attracts much attention because its fundamental
significance for understanding coherent phenomena in disordered media
and potential applications in optoelectronics because of easy
preparation (no need in mirrors) and small size down to several
microns. Since the first experimental demonstration by Cao and
coworkers in 1998 of the lasing emission from the ZnO nanopowder the
remarkable progress in studying the material, geometry and external
pumping dependences of laser properties and efficiency has been
reached. I will demonstrate that lasing occurs from the special random
cavities of high quality fromed within the active medium. They can be
described as the decaying eigen optical modes within the medium and
the optical mode having the minimum decay rate is responsible for
lasing. Numerical and analytical studies of the properties of these
modes permit to interpret existing experiments and suggest the ways to
optimize the performance of lasers.