What do bureaucrats respond to? What is bureaucratic discretion? We raised these two key questions at the end of Chapter 5. Then in Chapter 6 we provided a discussion of the role of organizational structure in NPDES enforcement. In this chapter we fill in the remaining pieces of the puzzle by examining in detail the nature of surface-water pollution control's regulatory environment. We first discuss a number of diverse factors that bureaucrats may respond to. Then we provide an empirical test of the regulatory diversity thesis.