In this collection, archaeologists, historians, geographers and language specialists re-examine the structure and political development of Celtic states scattered across present-day Europe. The main theoretical focus is on whether and when state-level complexity was attained in the different Celtic settlements. The contributors also discuss and evaluate the various methods for studying Celtic social systems: the historical textual studies, as opposed to the analysis of the archaeological record, and the use of regional comparisons. Interweaving archaeological and textual evidence, the result is an interdisciplinary study of state formation never before attempted on such a wide scale which contributes to our understanding of social complexity in Celtic Europe, and, more generally, to the processes underlying social transformation.