The Standard Model predicts that the photons emitted in flavor-­‐changing neutral current b to s gamma transitions are predominantly left-­‐handed. However, the photon polarization has never been observed in a direct measurement and remains largely unexplored. Several extensions of the Standard Model predicting a significantly different photon polarization have not been yet ruled out by other measurements, such as the inclusive B to Xs gamma decay rate. Among other topics, this talk will focus on the recent study of the radiative B to K pi pi gamma decays performed using data collected in pp collisions with the LHCb detector at 7 and 8 TeV center-­‐of-­‐mass energies. The distribution of the angle of the photon direction with respect to the plane defined by the final-­‐state hadrons in their rest frame is studied in intervals of K pi pi mass and the asymmetry between the number of signal events found on each side of the plane is presented. The first direct observation of the photon polarization in the b to s gamma transition is reported with a significance of 5.2 standard deviations.