Over the last forty years, legal theory and policy advice have come to draw heavily from an 'evolutionary' jurisprudence that explains legal transformation by drawing inspiration from the theoretical successes of Darwinian natural selection. This project seeks to enrich and critique this tradition using an analytical perspective that emphasizes the material consequences of concepts and ideas. Existing theories of legal evolution depend on a positivist epistemology that strictly distinguishes the objects of social life-interests, institutions, systems-from knowledge about those objects. My dissertation explores how knowledge, and especially non-legal expertise, acts as an independent site and locus of transformation, mediating the interaction between law and social phenomena and acting as a catalyst of legal innovation. Prior work by Simon Deakin has integrated insights from systems theory to show how the interaction between law and economic institutions can only be properly understood by attending to the epistemic frame law uses to interpret economic practice. Using a case study on the impact of 'law and finance' literature on World Bank policy advice and, consequentially, on legal reforms adopted by many developing countries between 2000 and the present, I show that such attention to legal knowledge is inadequate. The case points, first, to the contingency of the intellectual tools used to understand legal institutions. Rather than deploying a determinate rationality, private and public actors address legal, economic, and ethical problems using a variety of paradigms: viewpoints are not determined by realities. More fundamentally, the cases suggest that successful paradigms, rather than economic or political realities alone, shape the dynamics of socio-legal change. My conclusions address some normative questions that arise when researchers in a social scientific mode are implicated in the processes they seek to document. ed, Cambridge University Press 1995). The idea is traceable at least as far back as Hobbes: 'The law of such a society thus consisted of the commands of whoever was sovereign in that society. If law is the product of the human will, the process of legal change is simple. The sovereign decides to issue a new rule to replace the old rule; he has changed his mind.' Peter Stein, Legal Evolution: The Story of an Idea (Cambridge University Press 1980) 2. The modern inheritor of this strain of thinking about law, at least in the Anglo-American legal tradition, is HLA Hart. Hart's account of law is richer than Austin's. He does not traffic in the fiction that valid law can be identified with the will of a sovereign. He does nonetheless identify law with valid norms issued by a state-backed law-making authority, from which it follows that changes to law are definable as changes to those norms. Hart's seminal contribution to the positivist tradition is HLA Hart, The Concept of Law (Clarendon Press 1972).