This chapter reviews the available data - a huge amount of data indeed, the Alps being one of the most intensively studied belts in the world. It first characterizes the type of crustal material that was involved in the subduction process, in order to understand its previous history (lower crust, upper crust or both) and its location before the subduction (tilted blocks along the distal part of a palaeomargin, extensional allochthons). The chapter then reviews the basic knowledge about the high pressure-ultra-high pressure rocks in terms of P-T paths and timing. Finally, a discussion of the present geometry of the subducted continental units leads to some considerations about the kinematic evolution of the mountain belt. The Alpine belt displays numerous examples of subducted continental material. Structural considerations and timing data show that two distinct, unrelated, episodes of continental subduction have taken place.