  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 $\ell$ ($\ell$ different from the
characteristic) in time quasi-linear with respect to $\ell$. This is based in
particular on fast algorithms for power series expansion of the Weierstrass
$\wp$-function and related functions.
