The bimodality of type Ia Supernovae

We comment on the presence of a bimodality in the distribution of delay time between the formation of the progenitors and their explosion as type Ia SNe. Two "flavors" of such bimodality are present in the literature: a weak bimodality, in which type la SNe must explode from both young and old progenitors, and a strong bimodality, in which about half of the systems explode within 108 years from formation. The weak bimodality is observationally based on the dependence of the rates with the host galaxy Star Formation Rate (SFR), while the strong one on the different rates in radio-loud and radio-quiet early-type galaxies. We review the evidence for these bimodalities. Finally, we estimate the fraction of SNe which are missed by optical and near-IR searches because of dust extinction in massive starbursts.