Tsetse ( SEET-see, US: TSEET-see or UK: TSET-sə) (sometimes spelled tzetze; also known as tik-tik flies), are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus Glossina, which are placed in their own family, Glossinidae. The tsetse is an obligate parasite, which lives by feeding on the blood of vertebrate animals. Tsetse has been extensively studied, because of their role in transmitting disease. They have a prominent economic impact in sub-Saharan Africa, as the biological vectors of trypanosomes, causing human and animal trypanosomiasis.

Tsetse can be distinguished from other large flies by two easily-observed features: Primarily, tsetse fold their wings over their abdomens completely when they are resting (so that one wing rests directly on top of the other); Secondly, tsetse also have a long proboscis, extending directly forward, which is attached by a distinct bulb to the bottom of their heads.

Fossilized tsetse has been recovered from Paleogene-aged rocks in the United States and Germany. Twenty-three extant species of tsetse flies are known from the African continent as well as the Arabian Peninsula.