  We summarize the presentations made within Working Group 3 of the CKM2021
workshop. This working group is devoted to rare $B$, $D$ and $K$ decays,
radiative and electroweak-penguin decays, including constraints on $V_{\rm
td}/V_{\rm ts}$ and $\epsilon^\prime / \epsilon$. The working group has thus a
very broad scope, and includes very topical subjects such as the coherent array
of discrepancies in semi-leptonic $B$ decays. Each contribution is here
summarized very succinctly with the aim of providing an overview of the main
results. The reader interested in fuller details is referred to the individual
contributions.
