In this proceeding we will review the current theoretical status of rare $B$ decays. These decays are indeed excellent indirect probes for New Physics searches, and in the current situation where no new states have been directly observed at collider, they provide a fundamental and alternative approach in the quest for Physics beyond the Standard Model. We will focus on the following classes of decays: $B_q\to\tau\nu$, $B_q\to\mu\mu$, $B\to K^{(*)}\nu\bar\nu$, $B\to K^{(*)}\ell\ell$, $B_s\to\phi\ell\ell$ and $b\to s\gamma$. The most updated Standard Model predictions will be provided, highlighting which are the main sources of uncertainty, and what is the possibility for New Physics effects when confronting the theory numbers to current experimental results.