In the revolution that marked the beginning of the English Commonwealth and Protectorates, law and the lawyers were subject to devastating challenge. Radicals, perceiving a failure of the law to guard the liberties of the subject, demanded sweeping changes which Oliver Cromwell and succeeding parliaments consistently threatened to implement. Yet these attacks were not against the law as law. Through political discourse and the imagery of legal ceremony, Interregnum governments invoked the authority of law. The law was a scene of contention as protagonists of various persuasions sought to possess it. Lawyers were therefore under enormous strain. This thesis will study that strain, the responses of the lawyers as a whole and, where possible, as individuals, to the competition for the sanction of legal authority. The key element of the lawyers' response was the refinement of a professional ideology characterised by a rigorous attention to form and precedent. That ideology ran counter to early seventeenth-century advances in the study of legal history which in turn supported the legal positivism so important to the intellectual underpinnings of the republic. Though John Selden is considered to be the better jurist, Sir Edward Coke's ancient constitutionalism offered lawyers the tools to preserve the shape of a law in which they held a proprietary interest. That ideology had political and professional consequences. In parliament, lawyers placed a conservative stamp on the direction of constitutional development. Partly in reaction to the instability occasioned by a plethora of constitutional innovations, partly out of their faith in the old forms of the past, lawyers tended to impede parliamentary business in the early 1650s. However, under the more conservative 'Humble Petition' and Advice of 1657, lawyers acted pragmatically. They saw in that constitutional package progress towards their goal of a restoration of the monarchy if not of Charles II. Professionally, the lawyers' ideology justified service in the courts of a usurping power. After 1642, patterns of practice in the courts changed little. This continuity testified to the pre-eminence the profession gave to the law over the state, as well as to the success of the bench in insulating the courts from reformist fervour