In Georgetown's MPP website it states one has to chose one of three paths: Economic and Social Policy (ESP), Management and Leadership (ML) or International Policy and Development (IPD) and in the case of IPD it also says that one "must take at least one of four “selectives” in this area to satisfy the concentration, in addition to international/comparative sections of the Process and Public Management core courses". What are three divisions differences course wise? What are the four selectives? I want to specialize in environmental policy which one should I follow?