Supernova statistics, establishing a direct link between stellar populations and explosion scenarios, is a crucial test of stellar evolution theory. Nowadays, a number of SN searches in the local Universe and at high redshifts are allowing observational probes of long standing theoretical scenarios. I will briefly review some of the most interesting results in particular for what concern the evolution with cosmic time of the SN rate, which is one of the topic that in the last few years had a most rapid development.

The Supernova Working Group was re-established at the IAU XXV General Assembly in Sydney, 21 July 2003, sponsored by Commissions 28 (Galaxies) and 47 (Cosmology). Here we report on some of its activities since 2005.

The statistics of SN discoveries is used to reveal selection biases of past and current SN searches and to gain insight on the progenitor scenarios for the different SN types. We also report estimates of the SN rate per unit mass in galaxies of different types and on the first attempts to study the evolution of the supernova rate with redshift.

New values of the frequencies of SNe are presented and discussed in relation to their use as SF indicators. The rate of core-collapse SNe is correlated to the colors and the FIR excesses of the parent galaxies in the sense that galaxies with blue colors and strong infrared excess have higher occurrence of type II and Ib/c SNe than other galaxies. This is in agreement with the expectation that they contain a higher fraction of massive stars. Instead no correlation is present for SNIa. The SN frequency does not correlate with the galaxy activity probably because searches are unable to discover SNe in the nuclear regions of galaxies.

A number of SNe with spectra similar to those of AGN exist. Their characteristic features are explained with explosion of SNe in dense environments, reminding of cSNR's invoked in the starburst model for AGNs. Some recent, peculiar SNe seem linked to GRB's opening the possibility that at least some GRB's arise from this kind of stellar explosion.

The rate of supernovae (SNe) is a key number linking stellar evolution with galaxy evolution models. Stellar evolution theories predict life times, fates and nucleosysntesis yields of individual stars which are used to predicted the galaxy chemical evolution once the star formation history in the galaxy is known. Constraints to the models are the present chemical content of galaxies but also the present observed SN rate (Arimoto & Yoshi, 1987; Ferrini & Poggianti, 1993; Matteucci, 1994; Renzini et al., 1993; Bressan et al., 1994; Elbaz et al., 1995).