  These TASI lectures where given in 2018 and provide an introduction to the
Strong CP problem and the axion. I start by introducing the Strong CP problem
from both a classical and a quantum mechanical perspective, calculating the
neutron eDM and discussing the $\theta$ vacua. Next, I review the various
solutions and discuss the active areas of axion model building. Finally, I
summarize various experiments proposed to look for these solutions.
