Pathological tau protein is found in Alzheimer's disease and related tauopathies. The protein is hyperphosphorylated and/or mutated which leads to aggregation and neurotoxicity. Because cognitive functions correlate well with the degree of tau pathology, clearing these aggregates is a promising therapeutic approach. Studies pioneered by our laboratory and confirmed by others have shown that both active and passive immunizations targeting disease-related tau epitopes successfully reduce tau aggregates in vivo and slow or prevent behavioral impairments in mouse models of tauopathy. Here, we summarize recent advances in this new field.