In this contribution, we provide an overview of some of the strategies for maximising the luminescence efficiencies of simple square-planar platinum(II) complexes in solution, including the introduction of strong-field co-ligands into di- and tri-imine complexes, involvement of intraligand charge-transfer excited states, and cyclometallation. We then explore in more detail several classes of platinum(II) complexes containing cyclometallating bidentate and terdentate ligands, many of which are significantly luminescent in solution at room temperature. The background to the use of brightly emissive platinum(II) complexes as phosphors in organic light emitting devices (OLEDs) is discussed. Key recent studies on the use of Pt(II) complexes in OLEDs are reviewed.