Aside from being spectacular displays in their own right, Type Ia supernova explosions have a key role in measuring the expansion history of the Universe and synthesizing the iron group elements. But what is their origin? That Type Ia supernovae arise from exploding white dwarfs is relatively well-established but the nature of the stellar systems in which the explosions occur remains a hotly debated issue.

I will discuss the theoretical modelling of Type Ia supernovae and some of the developments made over the last few years. I will argue that understanding the diversity of Type Ia supernovae requires us to investigate a variety of different progenitor scenarios. In particular, I will focus on scenarios involving the explosion of sub-Chandrasekhar mass white dwarfs, a class of model which may yet have promise for explaining a significant fraction of the Ias.