A peculiar and most important property of Bs mesons is that they transform spontaneously into their own antiparticles, and back again. These transitions, known as flavor oscillations or mixing, are extremely rapid, rendering their measurement a very challenging experimental task. The determination of the Bs oscillation frequency is, at the same time, of great interest for constraining elements of the Standard Model CKM matrix and its unitarity. Large samples of Bs mesons collected by the CDF and D0 experiments operating at the Fermilab Tevatron have recently yielded unprecedented results, which are here reported. Emphasis is given to details of the analysis developed at CDF, presenting the observation of Bs mixing, the precise measurement of the oscillation frequency, and a discussion of its impact on the description of the flavor sector.
