  Recently the muonic hydrogen lamb shift has been measured with unprecedented
accuracy, allowing for a precise determination of the proton radius. This
determination is 5 sigma away from the previous CODATA value obtained from
(mainly) the hydrogen lamb shift and the electron-proton scattering. Within an
effective field theory formalism, I will define the proton radius and briefly
review some aspects of the theoretical prediction for the muonic hydrogen lamb
shift, studying both the pure QED-like computation and the hadronic effects.
