Teso (endonym Ateso) is an Eastern Nilotic language spoken by the Teso people of Uganda and Kenya and some speakers are in South Sudan. It is part of the Teso–Turkana language cluster.

According to the 2012 Uganda population and housing census, over 11.57 million people in Uganda (66.7 percent of the total Uganda population) spoke Ateso. Also, an estimated 279,000 people in Kenya speak the language. Its ISO 639-3 code is teo.

Ateso is spoken in the Teso sub-region. Ateso is also known as Bakedi, Bakidi, Elgumi, Etossio, Ikumama, Iteso, Teso or Wamia. It is closely related to Turkana and Karamojong.

There are 22 letters in the Ateso alphabet. The letters f, h, q, v, h, x and z are not used, while the alphabet includes additionally the letter ŋ and digraph ny. The above mentioned letters only appear in loanwords. The pronunciation guides that follow are for practice only; the correct sounds can only be learned by practice from a teacher or an audio media.

There are five vowels in Ateso: a, e, i, o, u. These five letters, however, represent more than five sounds. For the letters E, I, O and U have two values each; a "close" value and an "open" value.

Close vowels are pronounced approximately as follows:

Open vowels are pronounced approximately as follows:

Note that whether the root vowel is "closed" or "open" affects the conjugation of the verb.