In 2010 the proton charge radius was extracted for the first time from muonic hydrogen, a bound state of a muon and a proton. The value obtained was five standard deviations away from the regular hydrogen extraction. Taken at face value, this might be an indication of a new force in nature coupling to muons, but not electrons. It also forces to reexamine our understanding of the structure of the proton.

In this talk I will describe an ongoing theoretical research effort that seeks to address and resolve this "proton radius puzzle". In particular, I will present a reevaluation of the proton structure effects, correcting 40 years of such calculations, and the development of new theoretical tools that would allow to directly connect muonic hydrogen and muon-proton scattering.