  We establish the invariant trace formula (\`a la Arthur) for the ad\'elic
covers of connected reductive groups over a number field, under the hypothesis
that the trace Paley-Wiener theorem is verified for all Levi subgroups at the
real archimedean places. For instance, this hypothesis can be verified for the
metaplectic covers of GL(n), or the twofold metaplectic cover of Sp(2n). We
also give simple trace formulae when the test function satisfies certain
cuspidality properties.
