Is there more than one “Curie’s principle”? How far are different formulations legitimate? What are the aspects that make it so scientifically fruitful? This article is devoted to exploring these questions. We begin by discussing Curie’s original 1894 article. Then, we consider the way that the discussion of the principle took shape from early commentators to its modern form. We say why we think that the modern focus on the interstate version of the principle loses sight of some of the most significant applications of the principle. Finally, we address criticisms of the principle put forward by John Norton and Bryan Roberts.