This chapter reviews the standard virtues of scientific theories and introduces the scientific realism debate with a particular focus on simplicity. The chapter argues that the multi-facetedness and context-dependence of simplicity, contrary to the received view, does not undermine the potential of simplicity considerations to arbitrate theory-choice. The chapter furthermore proposes that concerns of simplicity can be justified via the ‘evidential-explanatory rationale’ which compels us to choose the theories whose postulated entities or principles are empirically supported in the explanation of the target phenomena. It is argued that the evidential-explanatory rationale for simplicity offers an argument for realism: since simpler theories are better supported empirically than complex ones (explaining the same evidence), simplicity, contrary to what the antirealist holds, is an epistemic concern. This is the ‘argument from simplicity’.