Community co-insurance is a contract which stems from European Law (Directives 78/473/EEC, 88/357/EEC, 2009/138/EC) and which has been subject to a troubled iter of transposition into the national laws of various Member States, having also received four condemnatory sentences from the Court of Justice of the European Union in 1986, for violations of art. 169 EEC Treaty (art. 226 EC Treaty) reported by the Commission. This paper, through a historical-juridical analysis on the phase of implementation of this Community law, will offer some observations from the comparison of various implementation laws, in particular with regard to the figure of the leading insurer. The aim is to understand the reasons for the limited application of this type of contract.