  I give an introduction to the theory of meson-antimeson mixing, aiming at
students who plan to work at a flavour physics experiment or intend to do
associated theoretical studies. I derive the formulae for the time evolution of
a neutral meson system and show how the mass and width differences among the
neutral meson eigenstates and the CP phase in mixing are calculated in the
Standard Model. Special emphasis is laid on CP violation, which is covered in
detail for K mixing, Bd mixing and Bs mixing. I explain the constraints on the
apex (rho-bar,eta-bar) of the unitarity triangle implied by epsilon_K, Delta
m_{B_d}, Delta m_{B_d}/(Delta m_{B_s}) and various mixing-induced CP
asymmetries such as a_CP(Bd-bar -> J/psi K_short)(t). The impact of a future
measurement of CP violation in flavour-specific Bd decays is also shown.
