What exactly is scientific explanation? ‘Explanation in science’ begins with Carl Hempel's covering law model of explanation, which says that to explain a phenomenon is to show that its occurrence follows deductively from a general law, perhaps supplemented by other laws and/or particular facts, all of which must be true. This model does not deal with symmetry or irrelevance. The covering law model implies that explanation should be a symmetric relation, but in fact it is asymmetric. Also, a good explanation of a phenomenon should contain information that is relevant to the phenomenon's occurrence. Causality-based accounts of scientific explanation and the concepts of reduction and multiple realization are also explained.