  We study the causal structure of a class of weakly nonlocal gravitational
theories (eventually coupled to matter) that are compatible with perturbative
unitarity and finiteness at quantum level. In particular, we show that in
nonlocal quantum gravity a Shapiro's time advance never occurs. Moreover, we
provide a recipe to construct a general ultraviolet complete gravitational
theory coupled to matter (with or without supersymmetry) compatible with
causality. Therefore, nonlocal gravity is consistent with causality, as well as
string theory.
