A subset of the real line is called a Cantor set if it is compact,
perfect, and nowhere dense. Cantor sets arise in many areas; in this
talk we will discuss their relevance in the spectral theory of
Schr\"odinger operators. We discuss several results showing that the
spectrum of such an operator is a Cantor set, from the discovery of the
first example by Moser to a genericity result by Avila, Bochi, and
Damanik. A Cantor measure is a probability measure on the real line
whose topological support is a Cantor set. A primary example in the
spectral theory context is the density of states measure in situations
where the spectrum is a Cantor set. A conjecture of Simon claims a
strict inequality between the dimensions of the set and the measure for
the Fibonacci potential. If time permits, we will discuss a recent
result of Damanik, Gorodetski, and Yessen, which establishes this
conjecture in full generality.