Microscopy plays a major role in the investigation of several diseases in human diagnostics and veterinary medicine. The microscopic analysis is mostly carried out in medical laboratories and requires specialised staff or expensive equipment. Therefore, providing results is time-consuming and far from the point-of-care where a fast diagnosis can be life-saving. Especially in infrastructural underdeveloped areas, with a lack of medical facilities and expert knowledge, this drawback is visible. Because of this, researchers started to develop "mobile microscopes" that can be used with a smartphone to enable everyone to be a specialist. This review is meant to give an overview about developed smartphone based mobile microscopes, their different construction methods, their technical advantages and disadvantages, their possible diagnostic applications and their limitations.