This thesis explores the ways in which professionals (in particular, social work professionals) define, produce, transfer, use, develop and disseminate knowledge of and for their profession and their practice. The thesis considers the issue(s) of professional knowledge from three related but distinct perspectives: philosophical, methodological and professional. From a philosophical perspective, the thesis articulates and examines the underpinning principles of epistemology and considers to what extent the professional social work knowledge debate has been informed by reference to these, and whether the application of appropriate epistemic principles has anything to offer the professions(s) in terms of its knowledge requirements. Methodologically, the thesis is informed by the history of the philosophy of science regarding the nature of inquiry. These considerations provide a clear paradigmatic rationale and context for the utilisation of a mixed-methods approach to the empirical content, with Q-Factor analysis being the quantitative method of choice, supported by semi-structured interviews. From a professional perspective, the thesis explores the views of those professionals actively engaged in those processes of defining, producing, transferring, using, developing and disseminating knowledge of and for social work. These three perspectives are here combined to provide a means by which the views and understandings of professionals can be articulated in meaningful ways and used to inform future discussion and practice regarding professional knowledge forms. The findings within this thesis reveal the differing ways professional social workers both theorise about and engage with knowledge in its many and varied forms. The findings also highlight the ways in which influences external to the individual affect how knowledge is, or is not used, and how some forms of knowledge appear to have preferential status. The conclusions suggest ways of responding to and addressing these issues by reference to a new pragmatic epistemology for the profession(s), which takes cognisance of the contemporary professional zeitgeist.