Under German law, standard business terms (German Allgemeine Geschäftsbedingungen, Swedish allmänna villkor) are regulated by contract law, namely sections 305 to 310 of the German Civil Code (BGB). The law imposes, inter alia, requirements as to the content of standard business terms. As part of contract law, these provisions have an effect only on the parties to a contract and formally do not affect third parties. Third parties may, however, be actually affected by standard business terms. In practice, this is particularly relevant in competitive situations where standard business terms do not comply with the legal requirements and may thus be considered illegal. Consider that companies compete with each other and one of them uses illegal standard business terms. Under these circumstances, the question can be raised whether competitors as third parties may invoke legal remedies against the company using such terms. Using illegal standard business terms may provide competitive advantages since they rationalize contracts and pass on risk to the other parties beyond what is allowed by law. Legal remedies of competitors may be found in the German Unfair Competition Act (UWG). It is, however, controversial whether competitors may file for injunctive relief against the company using illegal standard business terms. Required is a violation of a provision of law which is intended to regulate the market behaviour in the interests of market participants. Sections 307 to 309 BGB, which relate to the content of standard business terms, may represent such provisions of law. Still, the German Federal Supreme Court (BGH) has yet to decide on this matter. This dissertation therefore tries to analyse and assess the different existing approaches and is even developing a new approach to this question. The analysis focuses on section 4 No.11 UWG and investigates whether sections 307 to 309 BGB actually intend to regulate the market behaviour in the interest of market participants. It will be shown that sections 307 to 309 BGB provide a level playing field for all competitors as regards the rationalization of contracts and the passing on of risk. They consequently protect not only the other party to a contract but also competitors as third parties. This quite surprising finding illustrates that competition law and contract law, in this context, have significant similarities and overlaps. For this reason, the general relationship between these two fields of law will be analysed and studied in detail as well.