Lepton flavour universality in charged-current $B$ decays

Tests of lepton flavour universality in charged-current $B$ decays offer an excellent opportunity to test the Standard Model, and show hints of new physics in analyses performed by the LHCb, Belle and BaBar experiments. These proceedings present the results from the LHCb collaboration on measurements of $\mathcal{R}(D^*)$ and $\mathcal{R}(J/\psi)$. It also presents the latest semileptonic tag measurement of $\mathcal{R}(D)$ and $\mathcal{R}(D^*)$ by the Belle collaboration. The latest HFLAV average shows a discrepancy of 3.1$\sigma$ between the Standard Model predictions and combined measurements of $\mathcal{R}(D)$ and $\mathcal{R}(D^*)$.