  This is the written version of four lectures given at the 1994 TASI. My aim
is to explain the essentials of lattice calculations, give an update on (though
not a review of) the present status of calculations of phenomenologically
interesting quantities, and to provide an understanding of the various sources
of uncertainty in the results. I illustrate the important issues using the
examples of the kaon B-parameter ($B_K$) and various quantities related to
$B$-meson physics. Contents: 1. Why do we need lattice QCD? 2. Basics of
Euclidean Lattice Field Theory. 3. Discretizing QCD. 4. Simulations. 5.
Numerical Results from quenched QCD. 6. Anatomy of a calculation: $B_K$. 7.
Heavy mesons on the lattice. 8. A final flourish
