The document discusses definitions and etiology of in-stent restenosis as well as treatments for it. It defines angiographic, IVUS/OCT, and pathological definitions of restenosis. It also discusses mechanisms of in-stent restenosis including mechanical causes like underexpansion and biological causes like neointimal hyperplasia. The document then summarizes various treatment strategies for in-stent restenosis such as plain balloon angioplasty, atherectomy, brachytherapy, repeat stenting, and drug-coated balloons. It provides details on studies comparing the effectiveness of these different treatment methods.