  Planet-forming disc evolution is not independent of the star formation and
feedback process in giant molecular clouds. In particular, OB stars emit UV
radiation that heats and disperses discs in a process called 'external
photoevaporation'. This process is understood to be the dominant environmental
influence acting on planet-forming discs in typical star forming regions. Our
best studied discs are nearby, in sparse stellar groups where external
photoevaporation is less effective. However the majority of discs are expected
to reside in much stronger UV environments. Understanding external
photoevaporation is therefore key to understanding how most discs evolve, and
hence how most planets form. Here we review our theoretical and observational
understanding of external photoevaporation. We also lay out key developments
for the future to address existing unknowns and establish the full role of
external photoevaporation in the disc evolution and planet formation process.
