The uncertainties of the current power system with a larger share of renewables and more volatile generation profiles increases the importance of assessing resource adequacy. Within this framework, the thesis “Evaluation of missing capacity and resource adequacy in an interconnected power system” aims to answer the following question: “How to reach reliability targets in the interconnected European power system?". To answer this question the concept of Missing Capacity is introduced as a possible adequacy indicator that quantifies the required capacity to reach a pre-defined reliability target in a specific region. The evaluation of missing capacity can be classified by the area of study, i.e. single or multi-area, and by the capacity expansion source, i.e. generation and/or interconnection capacity expansion. Following such classification, a methodology for the evaluation of Missing Capacity is presented. Furthermore, by analyzing the transmission capacity expansion approach the contribution of interconnectors to system adequacy is investigated.