The mathematical nature of modern physics suggests that mathematics is bound to play some role in explaining physical reality. Yet, there is an ongoing controversy about the prospects of mathematical explanations of physical facts and their nature. A common view has it that mathematics provides a rich and indispensable language for representing physical reality but that, ontologically, physical facts are not mathematical and, accordingly, mathematical facts cannot really explain physical facts. In what follows, I challenge this common view. I argue that, in addition to its representational role, in modern physics mathematics is constitutive of the physical. Granted the mathematical constitution of the physical, I propose an account of explanation in which mathematical frameworks, structures, and facts explain physical facts. In this account, mathematical explanations of physical facts are either species of physical explanations of physical facts in which the mathematical constitution of some physical facts in the explanans are highlighted, or simply explanations in which the mathematical constitution of physical facts are highlighted. In highlighting the mathematical constitution of physical facts, mathematical explanations of physical facts deepen and increase the scope of the understanding of the explained physical facts. I argue that, unlike other accounts of mathematical explanations of physical facts, the proposed account is not subject to the objection that mathematics only represents the physical facts that actually do the explanation. I conclude by briefly considering the implications that the mathematical constitution of the physical has for the question of the unreasonable effectiveness of the use of mathematics in physics. Outline 1 The orthodoxy 2 An alternative perspective 3 On the relationship between mathematics and physics 4 On conceptions of mathematical constitution of the physical 5 On the common view of how mathematical models represent physical reality 6 On the notion of the physical 7 On the scope of the mathematical constitution of the physical 8 A sketch of a new account of mathematical explanation of physical facts 9 On mathematical explanations of physical facts 9.1 On a D-N explanation of the life cycle of 'periodical' cicadas 9.2 On structural explanation of the uncertainty relations 9.3 On abstract explanation of the impossibility of a minimal tour across the bridges of Königsberg 9.4 On explanations by constraints that are more necessary than laws of nature 10 Is the effectiveness of mathematics in physics unreasonable?