A luminaire for installing in a grid ceiling includes at least one catch which is arranged in such a way on the luminaire and designed such that the at least one catch snaps into place automatically behind a portion of an element of the grid ceiling and thus engages behind the portion of the element of the grid ceiling in order to hold the luminaire on the grid ceiling. In addition, an assembly for a grid ceiling includes at least one ceiling profile element and at least one such luminaire.