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 \kkm, \bbmd\ and \bbms. I explain the constraints
on the apex $(\ov \rho,\ov \eta)$ of the unitarity triangle implied by
$\e_K$, $\dm_{B_d}$, $\dm_{B_d}/\dm_{B_s}$ and various mixing-induced
CP asymmetries such as $a_{\rm CP} (\ov B_d \to J/\psi K_{\rm
short})(t)$.
The impact of a future measurement of CP violation in flavour-specific
$B_d$ decays is also shown.
