"B_d and B_s mixing: mass and width differences and CP violation"

B--B-bar mixing involves three physical parameters: the off-diagonal
elements of the mass and decay matrices and their relative phase.  They
are related to the mass and width differences between the mass eigenstates
and to the asymmetry which quantifies CP violation in mixing. I present an
update of the theory predictions for these quantities in the Standard
Model and discuss how various present and future measurements can be
combined to constrain new physics.