Small firms are an important part of any economy, since they generate a large proportion of an economy's new jobs. Despite their apparent vitality, though, small firms are particularly vulnerable to the adverse effects of government regulation. Analyzing the impact of regulation on small firms is especially important for federal agencies in the U.S., since federal law requires agencies to conduct such studies. This study sets forth a simple economic theory of regulatory impact, and presents some tools that a regulatory body can use to evaluate the potential impact of a new regulation on small firms.