The European Target Model for electricity markets has been shaped over the past three decades by successive legislations and reforms with the aim of creating a liberalized integrated market fostering efficient cross border trade and competition. The operation of a single market requires the implementation of harmonized rules across the EU Member States as regards capacity allocation, congestion management and market coupling enabling cross-border exchanges of electricity. To this end, the majority of the EU countries have established organized markets, mainly power exchanges, operating in alignment with the EU Target Model rules facilitating energy transactions in a transparent and reliable manner. In 2020, Greece has adopted the necessary legislative and regulatory acts for the restructuring of the wholesale electricity market including the establishment of the Hellenic Energy Exchange operating the new markets, along with the Transmission System Operator. This thesis explores the EU background on the basis of which this major reform took place and presents the new regulatory framework for the operation of forward, day-ahead, intra-day and balancing markets for electricity, with a focus on the rules for access, participation and clearing of the transactions, followed by an assessment of the first year of the operation of the new markets.