Leptospirosis is a zoonotic disease of worldwide veterinary significance in many animal species. It is caused by infection with antigenically distinct serovars of the spirochete Leptospira interrogans sensu lato. Currently, over 250 different leptospiral serovars are known worldwide. These serovars can be further divided into pathogenic, non-pathogenic and opportunistic/ possibly pathogenic Leptospira. The preferred reservoir host and likely incidental host vary with the serovar as well as the geographic location. Laboratory testing is a critical component to aiding in the clinical diagnosis of this challenging disease. The microscopic agglutination test (MAT) is the reference test method for the serodiagnosis of leptospirosis both in humans and in animals. This test detects antibodies to specific serovars using live leptospiral antigens, and can be performed on serum from any species.