We survey algorithms for computing isogenies between elliptic curves defined
over a field of characteristic either 0 or a large prime. We introduce a new
algorithm that computes an isogeny of degree ℓ (ℓ different from the
characteristic) in time quasi-linear with respect to ℓ. This is based in
particular on fast algorithms for power series expansion of the Weierstrass
℘-function and related functions