The year 2013 marks a key milestone for the regional development of Romania, being at the same time the final year of the first programming period of the nonreimbursable assistance received by Romania as a fully-fledged member of the European Union and also a decisive year for the preparations for the future 2014 – 2020 programming period. This is the moment when both accomplishments and obstacles encountered in the last seven years should be analyzed in order to identify the lessons learned and to improve the future regional development process of Romania. In this context, this paper focuses on the concept of complementarity in the field of regional development. The purpose of the paper is to propose a theoretical model for identifying the complementarity links among regional development interventions, introducing a definition and a typology of this concept, along with some implementation means.