This paper explores explanatory practices of macro-historical social science in light of philosophical stances on determinism versus indeterminism. Analysis of determinism and its implications show its compatibility with practices emphasizing causal complexity, contingency, and choice. It can, moreover, clarify and contain these practices in ways that extend the priority traditionally given to causal explanation by macro-historical social scientists. Analysis of indeterminism shows, by contrast, that each of its major varieties challenge macro-historical explanatory practices. To embrace indeterminism and follow through its implications would, in effect, terminate the tradition of macro-historical inquiry as pursued by American sociologists and political scientists.