The rules presented in this volume of "Principles of European Law" deal with service contracts. The economic importance of service contracts within the European Union is enormous. The European Commission recently estimated that services account for some 50% of EU GDP and for some 60% of employment in the Union # though an exact figure is hard to determine given that many services are provided by manufacturers of goods. According to the European Commission, many services appear in official statistics as manufacturing activity, meaning that the role of services in the economy is often significantly underestimated. Drafting common principles on the law of services contracts is a novel experience. The existing codes only deal with a limited number of services and often provide only general provisions. Six categories were identified, of which some are close to legal tradition (construction, storage, and to some extent treatment). Others are an answer to challenges that come from the modern practice of contract law (processing, design, information). A first chapter provides general provisions common to all service contracts. Representation services will be dealt with in a separate volume. For each service contract, the principles aim at solving legal issues that arise as of the pre-contractual stage until the end of the contract's performance. Particular attention is given to co-operation duties and the information the parties need to exchange in order to increase the chances of their mutual satisfaction at any stage of their contractual relationship.