Using panel data from Denmark from 2001 to 2013, the authors find that serial entrepreneurs—those who open more than one business—have higher sales and greater productivity than do novice entrepreneurs—those who open only one business. Specifically, serial entrepreneurs' firms have 98% higher sales than the novices' firms, and serial entrepreneurs utilize more initial capital and labor, and thus are 49% more productive. Further, certain subsets of serial entrepreneurs perform especially well; those who hold a portfolio of overlapping firms or who open as limited liability corporations (LLCs) are top performers. The authors' findings suggest that 41% of LLC entrepreneurs are serial entrepreneurs, thus deepening the need to understand these types of entrepreneurs. Finally, female entrepreneurs are shown to realize sizable gains from serial entrepreneurship: The firms of both female and male serial entrepreneurs are twice as large as the firms of novice entrepreneurs of their respective gender.