  After reviewing the present experimental constraints on the unitarity
triangle, I discuss the various ways in which new physics can manifest itself
in measurements of the parameters of the unitarity triangle. Apart from one
exception, which I describe, new physics enters principally through new
contributions to B0-B0(bar) mixing. Different models of new physics can be
partially distinguished by looking at their effects on rare, flavour-changing
$B$ penguin decays. (Invited talk given at the Symposium Twenty Beautiful Years
of Bottom Physics, Chicago, IL, USA, June 29 -- July 2, 1997.)
