The thesis examines the transition from the Late Bronze to the Early Iron Age, i.e. the periods from Late Helladic IIIC (LHIIIC) to Protogeometric (PG) ( 1200-900 BC) in two areas of the Greek Mainland, the Argolid and Phokis-East Lokris. The Argolid, and in particular the Argive plain, which included among others the citadel of Mycenae, could be described as the core area of the Mycenaean world par excellence, while Phokis -East Lokris could be conventionally thought to belong to the Mycenaean periphery, since no palatial establishment was ever developed in the area. Through the comparative study of the evidence from the two areas, the different course of their post-palatial development is studied, and the factors that affected this development are carefully examined and discussed. In particular, the thesis investigates whether and how the different Mycenaean past of the two areas, and more specifically the different role of each one of them in the Mycenaean world affected their evolution in the period not only immediately after the palatial collapse but also in the transition to the Early Iron Age. The analysis of all the published evidence from LHIIIC to PG period (settlement remains, burials and cult evidence) offers a detailed view of the occupation of the areas in each phase of the transitional period and helps us gain a general, long-term understanding of settlement patterns, burial customs, cult practices and material culture. The study of continuity and changes in all these aspects also allows us to follow the socio-political evolution. In general, it is shown that the transition from the Late Bronze to the Early Iron Age was experienced very differently in each of the two areas under examination. The long-term view of the evidence as adopted by the present study, bridges the divide that scholarly literature has created between the two eras, while at the same time places the two areas in the general context of the Aegean. It also takes into account the significant role that external factors such as trade contacts or population movements played in this crucial period. Overall, this study stresses the individuality of each area and of each site of the Greek mainland, and demonstrates the complex historical reality of the transitional period and its many different components. The final aim of the thesis is to enlighten the transformation process that two different areas of the Greek mainland underwent from the post-palatial times until the beginning of the Early Iron Age, a process believed to carry the seeds for the rise of the most typical political formation of ancient Greece, the polis.