  We review the lives, deaths and nucleosynthetic signatures of intermediate
mass stars in the range approximately 6.5-12 Msun, which form super-AGB stars
near the end of their lives. We examine the critical mass boundaries both
between different types of massive white dwarfs (CO, CO-Ne, ONe) and between
white dwarfs and supernovae and discuss the relative fraction of super-AGB
stars that end life as either an ONe white dwarf or as a neutron star (or an
ONeFe white dwarf), after undergoing an electron capture supernova. We also
discuss the contribution of the other potential single-star channels to
electron-capture supernovae, that of the failed massive stars. We describe the
factors that influence these different final fates and mass limits, such as
composition, the efficiency of convection, rotation, nuclear reaction rates,
mass loss rates, and third dredge-up efficiency. We stress the importance of
the binary evolution channels for producing electron-capture supernovae. We
discuss recent nucleosynthesis calculations and elemental yield results and
present a new set of s-process heavy element yield predictions. We assess the
contribution from super-AGB star nucleosynthesis in a Galactic perspective, and
consider the (super-)AGB scenario in the context of the multiple stellar
populations seen in globular clusters. A brief summary of recent works on dust
production is included. Lastly we conclude with a discussion of the
observational constraints and potential future advances for study into these
stars on the low mass/high mass star boundary.

Solar and Stellar Astrophysics