A Nijenhuis operator on a manifold M is a (1, 1) tensor N whose Nijenhuistorsion vanishes. A Nijenhuis operator N on M determines a Lie algebroid structure (T M ) N on the tangent bundle T M . In this sense a Nijenhuis operator can be seen as an infinitesimal object. In this paper, we identify its global counterpart. Namely, we show that when the Lie algebroid (T M ) N is integrable, then it integrates to a Lie groupoid equipped with appropriate additional structure responsible for N , and viceversa, the Lie algebroid of a Lie groupoid equipped with such additional structure is of the type (T M ) N for some Nijenhuis operator N . We illustrate our integration result in various examples.