Despite growing attention to the issue of urban 'sustainability' and steady increases in the overall use of different renewable power technologies around the world, cities tend to have very low levels of 'green' power use or renewables technology deployment within their borders. Through field interviews and literature reviews, this thesis examines the factors that both help and hinder this situation, using New York City and London as case studies. New institutionalism and urban regime theories provide the analytical lenses through which the empirical research is viewed. Each theory examines this issue from a different perspective, with new institutionalism particularly adept at identifying explanations linked to the electric power sector's highly regulated policy environment. Urban regime theory (URT) emphasizes understanding who is involved in the policy-making and implementation process, and how their involvement influences any outcomes. Originally, URT was developed to analyze urban growth coalitions and other urban economic development activities, although researchers have more recently posited its applicability to a wide range of fields, including urban environmental policy-making. When examining energy policy-making in both London and New York, however, a traditional URT approach falls short because it does not easily accommodate the influence of formal regulatory mechanisms in shaping outcomes. By modifying URT, however, so it adopts aspects of a new institutionalist approach, highly compelling and comprehensive explanations for local energy policy and program decisions can be obtained. This thesis concludes by detailing circumstances under which this type of "Constrained" regime analysis is appropriate, and how its methodology differs from that of traditional urban regime theory.