Two-Photon Exchange: The experimental side

Two-photon exchange is the expected explanation of the proton form-factor ratio puzzle. Three recent experiments at DESY, VEPP-3 and JLAB aimed to measure this effect directly. In the talk, I will present the results of these experiments with focus on the OLYMPUS experiment at DESY. I will discuss the current state of affairs and outline possible future measurements at DESY (near term) and JLAB (long term).