Hard exclusive processes at HERMES

The production of mesons (or photons) in deep-inelastic lepton scattering gives access to information on the structure of hadrons that is otherwise hard to obtain. When the production process involves at least one hard scale and is exclusive, the data can be interpreted in terms of the recently introduced generalized parton distributions (GPDs). These GPDs provide a unified description of hadronic structure, which can be applied to many different reactions. It will be shown how new data collected by the HERMES experiment at DESY are used to obtain first information on GPDs. Examples of hard exclusive processes observed at HERMES include the production of pseudoscalar and vector mesons, and deeply-virtual Compton scattering