What do we mean by “science,” and why does it carry such authority in public debates and policy decisions? This chapter explores the evolving concept of science, particularly Western Science, and its privileged role in informing public policy. Beginning with the historical roots and diverse global interpretations of scientific knowledge, we explore how modern science emerged with institutional frameworks, standards of evidence, and communities of practice. Central to this narrative are the Mertonian ideals—Communalism, Universalism, Disinterestedness, and Organised Scepticism—which sustain the credibility and social role of scientists. The standards of proof vary across disciplines. Artificial intelligence and big data are altering the scientific method, and the challenges of communicating scientific uncertainty in policy contexts. The sociology of science is traced through the lenses of Popper's falsifiability, Kuhn’s paradigm shifts, and Latour’s Actor Network Theory. Ultimately, the chapter highlights the dual identity of scientists as both experts and citizens, and the ethical tensions they navigate when engaging in public discourse and policy-making.