Regulatory costs are an essential aspect of the efficiency and quality of regulations. Moreover, they are a genuine loss of welfare which have a negative impact on national income. Surprisingly, regulatory costs are often neglected or misinterpreted in regulatory assessments, except - though only recently - for administrative compliance costs. One important reason is the lack of a clear and consistent definition as well as a practical and exhaustive typology of regulatory costs. This conceptual paper presents a cost taxonomy that takes into account all costs of regulation. We identify 16 direct and 2 indirect regulatory cost types. The former are costs borne by society in preparing and implementing regulations. For the government, they consist of information, decision-making, drawing-up, planning, administrative start-up, operational, monitoring, and enforcement costs. Citizens and businesses, on the other hand, incur rent-seeking, information, planning, three types of compliance, delay and enforcement costs. The indirect costs comprise the efficiency loss plus, in the event of poorly designed or market-based regulation, also transaction costs. The neglect of any of these costs may lead to the underestimation of costs in absolute or relative terms and thus to inefficient regulatory choices.European Journal of Law and Economics 32/3, p. 341-356.