  Static properties of hadrons such as their radii and other moments of the
electric and magnetic distributions can only be extracted using theoretical
methods and not directly measured from experiments. As a result, discrepancies
between the extracted values from different precision measurements can exist.
The proton charge radius, $r_p$, which is either extracted from electron proton
elastic scattering data or from hydrogen atom spectroscopy seems to be no
exception. The value $r_p = 0.84087(39)$ fm extracted from muonic hydrogen
spectroscopy is about 4% smaller than that obtained from electron proton
scattering or standard hydrogen spectroscopy. The resolution of this so called
proton radius puzzle has been attempted in many different ways over the past
six years. The present article reviews these attempts with a focus on the
methods of extracting the radius.
