A　versatile　synthetic　strategy　for　the　preparation　of　multimetallic　oxynitrides　has　been　designed　and　here　exemplarily　discussed　considering　the　preparation　of　nanoscaled　zinc–gallium　oxynitrides　and　zinc–gallium–indium　oxynitrides,　two　important　photocatalysts　of　new　generation,　which　proved　to　be　active　in　key　energy　related　processes　from　pollutant　decomposition　to　overall　water　splitting.　The　synthesis　presented　here　allows　the　preparation　of　small　nanoparticles　(less　than　20　nm　in　average　diameter),　well-defined　in　size　and　shape,　yet　highly　crystalline　and　with　the　highest　surface　area　reported　so　far　(up　to　80　m2　g−1).　X-ray　diffraction　studies　show　that　the　final　material　is　not　a　mixture　of　single　oxides　but　a　distinctive　compound.　The　photocatalytic　properties　of　the　oxynitrides　have　been　tested　towards　the　decomposition　of　an　organic　dye　(as　a　model　reaction　for　the　decomposition　of　air　pollutants),　showing　better　photocatalytic　performances　than　the　corresponding　pure　phases　(reaction　constant　0.22　h−1),　whereas　almost　no　reaction　was　observed　in　absence　of　catalyst　or　in　the　dark.　The　photocatalysts　have　been　also　tested　for　H2　evolution　(semi-reaction　of　the　water　splitting　process)　with　results　comparable　to　the　best　literature　values　but　leaving　room　for　further　improvement.　©　2019　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim