The communitarization of immigration and asylum disciplines and the beginning of a common European Union policy in such areas will begin to create more favorable conditions for the integration of third country nationals who are legally resident, in the territory of the EU. The Tampere European Council of 1999 stressed the need to provide to nationals of third countries rights and obligations similar to those of EU nationals, in order to eliminate social, economic and cultural discrimination. This could be possible through the approximation of the legal status of third country nationals to that of EU nationals. To achieve this goal, there are adopted secondary norms of Community legislation on equal treatment for certain categories of citizens of third countries as refugees, the long-term residents, etc. Regulation EC No 859/2003 extended the effects of the provisions relating to the coordination of national social security regimes and to third country nationals. This European common policy took a new development with the Lisbon Treaty. One of the objectives of the common policy on immigration is the one which provides an equo treatment to third-country national who are legally resident in one of the Member States. This attitude finds concretization even to several articles of the European Charter of Fundamental Rights, which after the Lisbon Treaty has binding legal effects as it has the same legal value of the treaties. The Directive 2011/98/EU aims to establish a single procedure for third country nationals to obtain a combined permit for both residence and work, establishing a series of rights for third-country nationals who are legally resident in a Member State. This directive, in certain sectors, provides an equal treatment of third country nationals with those national. But the text of the directive provides also the cases when EU Member States may derogate from the application of the principle of equal treatment. This paper aims to analyze legal instruments adopted by the EU which recognize the principle of equal treatment of nationals of third countries with nationals, as well as the ways provided to implement this important principle.