Philosophers have long debated the deceptively complex question posed in our opening line, with no definitive resolution in sight. Hence, we make no pretence at offering a conclusive answer here. Nevertheless, most philosophers agree that science is not merely a body of knowledge. What makes chemistry, physics, biology or, more controversially (see Berezow & Campbell, 2013; Lilienfeld, 2012, for competing views), psychology sciences is not their substance matter, as one can investigate any of these disciplines either scientifically or nonscientifically. For example, alchemy, cold fusion, creation science and phrenology are subdisciplines housed within the domains of chemistry, physics, biology and psychology, respectively, but they are all decidedly unscientific. Yet what renders them unscientific, and what distinguishes them from scientific subareas within each of these broad fields of study?