This thesis argues for a sociologically observable equilibrium between the competing forces of legal unity and legal diversity within the European Union (EU) in order to conceptualise the contested process of the Europeanisation of law as a contingent, reciprocal one that has no endpoint in either uniformity or discontinuity. The main point of departure is the concept of legal culture, which provides for an institutionally-bounded and territorially-delimited jurisdiction with a unique socio-historical context. Member State legal cultures, within the overarching EU legal space, are conceptualised as a segmentary form of legal system-internal differentiation on the basis of territory, whereby communications originating in and pertaining to a particular Member State are conditioned in terms of the legal-cultural context of that Member State. This thesis argues that this "fragmentation" is a force of diversity within the Europeanisation process, which operates against a unifying force, understood here to be a similarly legal-system internal differentiation on the basis of areas of law and their related epistemic communities. This thesis advances the argument that, instead of viewing the existence of legal diversity within the EU as being essentially problematic for the process of Europeanisation of law, legal diversity should be reconceptualised as a productive counterweight to any purported legal unity in the EU and re-entered into the process in order to maintain its openness. While the concept of legal unity provides the framework for the operation of the Europeanisation process, that of legal diversity within that framework provides the means by which the process remains open-ended and fully contingent. Legal unity, in turn, is positioned as a counterbalance to legal diversity in that it places restraints upon the diversifying forces of both nationalism and fragmentation within the EU, thus maintaining the overarching framework within which the process of Europeanisation can occur. Legal "unity in diversity", conceptualised both as a precondition of the process of the Europeanisation of law and as a default aim, sits in stark contrast to the two main theoretical approaches to the Europeanisation of law, namely deracinated formalism and autochthonous culturalism. This thesis proposes a middle way that avoids the pitfalls of these two extreme schools of thought by operationalising the conundrum of unitas in diversitate in a way that both maintains the critical openness of the ongoing Europeanisation of law process, and facilitates a form of organically-evolving social validity for this process and the resultant legal structure of the EU.