It used to be an axiom in political science that American parties were weak. Now we are not so sure. During the 1980s and 1990s, the profession produced a great deal of theoretical and empirical work suggesting that U.S. political parties were “resurgent.” J. P. Monroe's book, The Political Party Matrix: The Persistence of Organization, provides an interesting twist on the new literature. It argues that party change is the result not so much of strengthening but of adaptation.