Few-body physics with polarized photons

I've been asked to give an overview of recent experiments with polarized photons. Polarization observables enhance interference effects that often remain hidden in spin-averaged, unpolarized measurements. Access to such interference effects allows us to tackle new problems and gain new insights. But, because the effects are often subtle, progress is almost always linked to calculations with reasonably sophisticated models. That automatically drives the attention to few-body systems where such calculations can be carried out with reasonable accuracy. There is quite a collection of new experiments with polarized γ-ray beams. I'm going to discuss the highlights from a few, focusing on those areas where polarization tells us something really new. Each of these experiments are the work of moderately large collaborations and their composition is given at the beginning of each section. We begin with a short review of polarized photon sources