 Philosophers of science and metaphysicians address various issues about laws, but the basic question is: What is it to be a law? Two influential answers are the systems approach (Lewis, 1973, 1983, 1986, 1994) and the universals approach (Armstrong, 1978, 1983, 1991, 1993). Other treatments include antirealist views (van Fraassen 1989, Giere 1999, Ward 2002, Mumford 2004) and antireductionist views (Carroll 1994 and 2008, Lange 2000 and 2009, Maudlin 2007). Beside the basic question, the recent literature has also focused on (i) whether laws are determined by matters of fact, (ii) the role laws play in the problem of induction, (iii) whether laws involve a strong form of necessity, and (iv) the role of laws in physics and how that contrasts with the role of laws in the special sciences.