Georgij Karlowich Kreyer (Russian: Гео́ргий Ка́рлович Кре́йер, Georgy Karlovich Kreyer) (November 26, 1887 – January 11, 1942) was a Russian and Soviet botanist and mycologist (lichenologist) born in Saint Petersburg. In academic publications, his name has been spelt variously Georgij Kalowic Kreyer, Georgij Karlowich Kreyer and (in Polish orthography) Georgij Karlowicz Kreyer. Between 1908 and 1910, he made extensive collections of lichens in the Mogilev Region of Belarus, between Orsha and Syanno, in the neighbourhood of the settlements of Smalyany, Bobromynichi (Vitebsk Region) and Selets.