  We consider a complex of tori of length 2 defined over a number field k. We
establish here some local and global duality theorems for the (\'etale or
Galois) hypercohomology of such a complex. We prove the existence of a
Poitou-Tate exact sequence for such a complex, which generalizes the
Poitou-Tate exact sequences for finite Galois modules and tori. In particular,
we obtain a Poitou-Tate exact sequence for k-groups of multiplicative type. The
general results proven here lie at the root of recent results about the defect
of strong approximation in connected linear algebraic groups and about some
arithmetic duality theorems for the (non-abelian) Galois cohomology of such
groups.
