What is the nature of female part-time employment in the European Union? Using data from the Second European Survey on Working Conditions , the author seeks to address this question. The paper examines four regimes of part-time employment. The gender-roles model, which assumes that women work parttime because they are secondary earners or have children at home, ranks first as a predictor of the likelihood that a woman will work part-time. In the responsive firms model, which ranks second in explanatory power, part-time work is primarily seen as the firms' response to workers' demands for fewer working hours. The optimal staffing model assumes that employers will create part-time jobs as a response to the demand for time-related services; it ranks third in explanatory power. Finally, the secondary-labor market model, which assumes job insecurity, poor wages, and poor working conditions, ranks fourth in predicting whether a woman will work part- or full-time.