  I review the current status of understanding the mechanism of the nonmesonic
weak decays (NMWD) of hypernuclei. Long standing problem on the Gamma_n/Gamma_p
ratio has been solved by considering short-range weak interactions properly.
This leaves a few remaining problems, such as the asymmetry of the emitted
proton with respect to the Lambda polarization and validity of the Delta I=1/2
in the nonmesonic weak decay.
