In this day and age of europeanisation and internationalisation of all aspects of society, including law, the topic of medieval maritime law has attracted increasing interest.  Regulating sea shipping, which is characterised by the connection between different ‘nations’, sea law is intrinsically international.  Or is it?  The existence of a common medieval maritime law has often been presumed, but is researched thoroughly for the first time in this study. By analysing the developing and spread of the written sea laws across Northern Europe and by comparing the contents of the different maritime regulations, as well as the legal practice in five Northern European towns (Lübeck in Northern Germany, Reval (Tallinn) in Estonia, Danzig (Gdansk) in Poland, Kampen in the Netherlands and Aberdeen in Scotland) by using the examples of shipwreck, jettison and ship collision, the author has aimed to determine whether it is accurate to speak of a common law of the sea in medieval Northern Europe on the level of the books of law, their contents and the practice of the law at the town courts. Research has proven that there was no uniformity on any of these levels, despite occasional similarities between the laws and the judgements passed by the courts.  There was no single law compilation available throughout Northern Europe at any time during the Middle Ages, there were no common regulations in the written laws and there was  no uniform legal practice in the towns of Northern Europe. The divergence between the five towns handled in this study could largely be explained by the different role each of the towns played on the European stage.