The aim of this thesis is to shed light on the beginning of the Early Iron Age in Greece (1100 – 900 BC), the so-called Protogeometric period. This period was characterised by social regression, but also by partial and incipient recovery and increased population mobility. The region of focus is Thessaly (central Greek mainland), which constituted the northern margin of the old Mycenaean world and was, therefore, affected by the decline and disintegration of the Mycenaean civilisation. My main aim is to reconstruct social structure and social change in EIA Thessaly through the study of burial practices, dietary variation, and population movements. It is essential to understand how people related to the Mycenaean traditions, how they adapted to new living conditions, how they organised their social life and whether they were affected by population movements.I employed two different methods, the carbon, nitrogen, sulfur, and strontium isotope analysis of human skeletal material for the reconstruction of diet and population movements, and the contextual analysis of mortuary practices. The main conclusions of my research are as follows. The contextual analysis of the mortuary data revealed mainly subtle variation rather than rigid divisions between the different social groups in the Protogeometric period. The analysis of differences in dietary preferences did not produce any rigid patterns, but rather subtle differentiation, which corresponds well with the analysis of mortuary variation. Population mobility was attested in the beginning of the Early Iron Age as newcomers have been identified in the populations studied here; we cannot, however, yet trace the provenience of these individuals.