Abstract: Philadelphia has more than a dozen business improvement districts, entities commonly called BIDs.' The papers in this Symposium describe each of them in some detail. This kind of study is both valuable and unusual. Although BIDs have been subject to academic analysis in general terms,2 this Symposium offers the first examination that I know of the different BIDs within a single city. It thereby enables a comparative view within one legal system of what a BID is and what it does. My focus here will concentrate on one question concerning Philadelphia's BIDs: in creating these kinds of institutions, whom exactly has the legal system authorized to tap precisely what kinds of resources to do what? As I argue below, Philadelphia's BIDs offer a wide variety of answers to each of the elements in this question. These differences generate for me a puzzle—why have so many different neighborhoods adopted the same legal form to accomplish such different objectives? I turn to this puzzle below, after I examine the differences among Philadelphia's BIDs.