The recent developments in using iridium(III) complexes as phosphorescent emitters in electroluminescent devices, such as (white) organic light-emitting diodes and light-emitting electrochemical cells, are discussed. Additionally, applications in the emerging fields of molecular sensors, biolabeling, and photocatalysis are briefly evaluated. The basic strategies towards charged and non-charged iridium(III) complexes are summarized, and a wide range of assemblies is discussed. Small-molecule- and polymer-based materials are under intense investigation as emissive systems in electroluminescent devices, and special emphasis is placed on the latter with respect to synthesis, characterization, electro-optical properties, processing technologies, and performance.