I will present analytical formulations for the rate of Type Ia supernovae,
which describe the events for both the single and the double 
degenerate models for the SNIa progenitors. Such theoretical rates 
follow from general considerations on the evolution of binary systems, 
and can be easily implemented in codes which describe the evolution of 
stellar systems. 
I will show how the SNIa rate observed in galaxies of
different morphological types can be used to constrain the SNIa 
progenitor model.
I will also show some simplified applications of the formalism to
a few astrophysical problems, including the timescale for Fe enrichment
in galaxies, the cosmic evolution of the SNIa rate, the Fe enrichment
of the ICM.