  We study metric spaces homeomorphic to the 2-sphere, and find conditions
under which they are quasisymmetrically homeomorphic to the standard 2-sphere.
As an application of our main theorem we show that an Ahlfors 2-regular,
linearly locally contractible metric 2-sphere is quasisymmetrically
homeomorphic to the standard 2-sphere, answering a question of Heinonen and
Semmes.
