  The Levine-Tristram signature associates to each oriented link $L$ in $S^3$ a
function $\sigma_L \colon S^1 \to \mathbb{Z}.$ This invariant can be defined in
a variety of ways, and its numerous applications include the study of unlinking
numbers and link concordance. In this survey, we recall the three and four
dimensional definitions of $\sigma_L$, list its main properties and
applications, and give comprehensive references for the proofs of these
statements.
