Phenomenology from the Lattice

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