FLAG: Lattice QCD Tests of the Standard Model and Foretaste for Beyond

After a short presentation of the FLAG collaboration, we review lattice results related to pion, $K$-, $D$- and $B$-meson physics with the aim of making them easily accessible to the particle-physics community. Only a selection of FLAG averages or estimates is presented. For light flavours, we present results on the form factor $f_+(0)$, arising in semileptonic $K \rightarrow \pi$ transition at zero momentum transfer, as well as the decay-constants $f_K,f_\pi$ and their ratio. The consequences of these results for the CKM matrix elements $|V_{us}|$ and $|V_{ud}|$ are discussed. For heavy flavours we focus on $D$- and $B$-meson decay constants and form factors, as well as the CKM matrix elements $|V_{cs}|$, $|V_{cd}|$ and $|V_{ub}|$. In addition we briefly cover the recent advances stemming from the calculation the $B_K$-parameters and touch upon related current results relevant to the Physics beyond the Standard Model, which will be the subject of the next FLAG edition.