Described herein is modular luminaire assembly (100) which is readily assembled and installed in the field whilst providing rigidity, structural integrity and water-tightness. The assembly (100) comprises a plurality of luminaire modules (120) mounted on a supporting pole (110). The plurality of luminaire modules comprises three luminaire modules (130, 140, 150) which are connected to one another by respective module connectors (160, 170) and to the supporting pole (110) by module connector (180). Each luminaire module has at least one interface for engaging with a complementary interface of an adjacent luminaire module or the supporting pole (110) to provide a water-tight connection, each pair of modules being fixed together by a module connector.