  The importance of rare $K$ decays especially in the context of a kaon
unitarity triangle (KUT) is emphasized. The decay $K_L \to \pi^0 \nu \bar \nu$
is theoretically very clean but experimentally extremely challenging. The
Standard Model prediction $\mathcal{B}\sim 3 \times 10^{-11}$ is still about
two orders of magnitude away from the current experimental upper bound. One way
to continue to make progress towards the construction of a KUT is by improving
the accuracy in the calculation of $\varepsilon'$. Another way which is the
primary focus here is via studies of $K^0 \to \pi^0 \mu^+ \mu^-$. LHCb, J-PARC,
the proposed HIKE project, phenomenology, and in fact precision studies on the
lattice can all play a very important role in this context.
