The term “mootness” refers to a category of related precepts that preclude a reviewing court from reaching the underlying merits of a controversy. While questions dog this doctrine’s constitutional and prudential forms outside of the Bankruptcy Code’s ambit, few doubt either’s general validity. However, within bankruptcy’s periphery, more substantive questions abound. There, constitutional mootness’s recognizable form blurs, and the prudential doctrine dubiously known as equitable mootness resists pragmatic simplification.