We observed lasing in highly disordered gain media. The coherent feedback for lasing is supplied by recurrent light scattering. We studied in detail the dependence of random laser on the transport mean free path, the gain volume, and the sample size. A model based on the concept of quasistates is developed to explain the behaviors of random lasers. We also demonstrated the difference between random lasers with resonant feedback and random lasers with nonresonant feedback. With an increase in the amount of scattering, we showed the transition from lasing with nonresonant feedback to lasing with resonant feedback.