The proposal that the merger of two white dwarfs would form a major channel for the formation of hot subdwarfs has been current for over two decades. Naturally, such a merger would result in a single star, rather than a binary. The consequences for frequency, mass distribution, rotation velocity, surface composition, and so on are less obvious. In this talk I will review the general picture of double white dwarf mergers, including links between white dwarf mergers  and various classes of evolved star. It will present recent work on: 

a) links between main-sequence binaries and double white dwarf merger progenitors,

b) stellar evolution calculations following the merger of two white dwarfs, and

c) the correlation between predicted and observed surface abundances of post white-dwarf mergers.