The development of multidisciplinary Health Services Research and Health Technology Assessment in the United Kingdom in the 1990s informs government R&D policy for a ‘knowledge-based health service’. This thesis comprises health service case studies focused on medical techno-practice in a collection of eight publications and an original critical review essay. A wide variety of primary and secondary research methods are used in separate empirical studies. Perspectives from sociology applied to medicine and health care, science and technology studies (STS), and the multidisciplinary field of ‘health services research’ are combined to offer a detailed and reflexive account. Health care is a field of policy and technical practice marked by complex, hybrid problems, as well as being associated with a wide variety of benefits, hazards and socially perceived risks. The case studies examine three substantive fields of healthcare technology and practice affecting large proportions of the population: human implant technology (total hip prostheses); cancer detection (testing for early-stage prostate cancer); and outpatient care. The inter-related objectives of the work are, firstly, to analyse variability in patterns of health care. This enables, secondly, analysis of techno-practice variations in terms of their implications for effectiveness of interventions, social patterns of health care consumption, risks to patients and health care policy. Thirdly, explanations for variability in practices and policies can be offered, which suggests the need, fourthly, for sociologically-informed approaches to analysing the introduction of ‘new technology’ and practice into healthcare systems. The final objective is to make the case for, and contribute to a socio-political analysis of the advance of the new healthcare sciences and their articulation with public policy in contemporary advanced health care systems. The results of the three case studies show the following. A proliferation of costly artificial hips evoked a national policy response that draws heavily upon health technology assessment evidence and processes. Early detection of prostate cancer presents dilemmas associated with surgical specialisation, and conflict between policy, clinical beliefs and practices. Outpatient care demonstrates tension between modernisation, evidentiality and the obduracy of shared socio-­clinical practices. The common threads drawing the case studies together are the observed variability in patterns of health care delivery and practice; underlying patterns of medical beliefs, professional work organisation and socialisation; the variable consequences for shaping of healthcare risks and benefits for patient populations; and linkages between healthcare innovation, modernisation and counteracting controls. The case studies highlight tensions between forces of innovation and countervailing state, professional or institutional forms of control over healthcare techno-practices. The review essay builds upon the published work to develop a reflexive understanding of the activity of healthcare science as a policy-related enterprise. It argues that healthcare evidentiality as represented by the new healthcare sciences, its proponents and its institutional vehicles, should be considered as having legitimating and regulatory functions. Evidentiality should thus be considered one of the societal forces that must be embraced by a socio-politics of the contemporary dynamics of healthcare innovation and governance. The original critical review essay accompanying the published work contributes to this enterprise.