Scientific explanations have been intensively studied by philosophers of science during the last five decades. Explanations of laws did not receive as much attention as explanations of particular facts. In this article, I present a model for one type of explanations of laws: reductions of laws to phenomena at a micro-level. Examples of such reductions can be found in the natural sciences (the ideal gas law is probably the most famous example here) and in the social sciences (e.g., reduction of macroeconomic laws to the behaviour of individual economic agents).