Toxoplasmosis, caused by an intracellular protozoan parasite, Toxoplasma gondii, is widespread throughout the world. The disease is of major medical and veterinary importance, being a cause of congenital disease and abortion in humans and in domestic animals.[1] In addition, it has gained importance recently due to toxoplasma encephalitis in AIDS patients.[2] T. gondii was discovered 100 years ago. Its identification was rapidly followed by the recognition that it was a human pathogen. During the past 100 years, the spectrum of diseases caused by this ubiquitous pathogen has expanded to include both congenital and acute infections as well as the recognition of diseases caused by this pathogen in the immune-compromised host. Recent data on behavioural changes in animals due to chronic toxoplasmosis is leading to research on the effect of this pathogen on the behaviour of humans.[3] Experimental studies on T. gondii have resulted in it becoming a model organism for studies on host pathogen interactions. Integration of clinical and experimental data on T. gondii should continue to lead to important insights into improvements in diagnosis for clinical management and vaccine development for control of toxoplasmosis.