All available evidence for architecture of the Neolithic Period in Thessaly, Greece, is assembled and synthesized. The traditional house-type concept used in previous studies is reviewed and shown to contain a number of theoretical and methodological weaknesses. A new theoretical approach is developed, which treats Neolithic architecture as an integral component of the overall cultural system, reflecting climatic conditions, building technology, social organization, household structure, religion and ideology. The existence of a separate Aceramic phase in Thessaly is questioned; the "pithouse" architecture of that phase is rejected for lack of evidence. The earliest Early Neolithic architecture appears to be a local development of rectilinear houses of wood and clay; pise, mud brick, and stone foundations were also used. Evidence for Middle Neolithic architecture is more abundant, and takes the form of house remains and clay house models. MN settlements consist of detached but closely grouped houses separated by lanes and common courts. Houses are typically small, one-room structures of square or slightly elongated plan. Mud brick on stone foundations, and pitched roofs, are typical. Households probably consisted of nuclear families. The so-called "megara" of the MN period are shown to be locally developed parched houses. The identification of the "Tsangli houses" with similar structures from Can Hasan 2B in Anatolia, and the posited migration from there into Thessaly, are rejected on the basis of an archaeological comparison of the architecture of the two sites. Limited data for the LN period suggest a shift to smaller, more nucleated settlements. Houses seem to be larger now than in the MN period; this may reflect either occupation by extended families or the existence of status distinctions. The traditional interpretation of LN Dimini as the fortified palace of a king is reconsidered in light of a discussion of the ''Homeric model" implicit in the original excavator's reasoning, and on the basis of recent excavations at that site. Remains of the Final Neolithic are extremely limited; the existence of an apsidal house at Rakhmani suggests affinities with the architecture of the early phases of the Early Bronze Age in the region.