The article focuses on the so-called principle of mutual recognition and its impact on the integration of service markets in the European Union. Mutual recognition is the principle of EU law under which member states must allow services that are legally provided in another member state also to be sold in their own territory. For the exporter, this means that a service legally provided in one EU country should not have to meet a second set of requirements in the country to which they are exporting. In her theoretical and empirical analysis, the author sets out to determine just how much room is still available for a further opening of service markets in EU member states. Szypulewska-Porczyńska concludes that this chiefly depends on the solutions adopted in the construction of the internal market. The article lists the main tools used for building the internal service market and classifies the existing solutions in the so-called Services Directive transposed by EU member states. In the first part of the article, the author discusses the principle of mutual recognition in comparison to other tools of the internal market and the relationships between them. Part two looks at the service market in terms of how these tools are used. The third part of the article classifies the solutions adopted in the Services Directive in terms of the tools used in building the internal market. Against this background, part four traces the integration of service markets in EU countries in the period from 2007, when the Services Directive was adopted, to 2010, the first year after the statutory deadline for transposing the directive. According to the author, there is still room for a further opening of service markets in EU member states. The internal service market is only partly based on the principle of mutual recognition, which offers substantial opportunities for a further integration of service markets. Progress made in the integration of service markets in EU countries after the adoption of the Services Directive shows that this regulatory change has not reversed a negative trend on the internal services market when it comes to the role of intra-EU trade in the overall trade of services, the author says.