The current status of the experimental measurements and theoretical predictions of the anomalous magnetic moment of the muon $a\mu$ is briefly reviewed. The emphasis is put on the evaluation of the hadronic contribution to $a\mu$ as it has the largest uncertainty among all Standard Model contributions. The precision of the hadronic contribution is driven by the input $e^+e- $ data predominantly from the $\pi^+\pi^-$ channel. Including the latest experimental data on $e^+e^-$ annihilation into hadrons from CMD2 and SND for the $\pi^+\pi^-$ channel and BaBar for multi-hadron final states, the updated Standard Model prediction disagrees with the measurement dominated by BNL by 3.3 standard deviations, with the theoretical precision exceeding the experimental one.