Studying the Indo-European languages means having a privileged viewpoint on diachronic language change, because of their relative wealth of documentation, which spans over more than three millennia with almost no interruption, and their cultural position that they have enjoyed in human history. The chapters in this volume investigate case-studies in several ancient Indo-European languages (Ancient Greek, Latin, Hittite, Luwian, Sanskrit, Avestan, Old Persian, Armenian, Albanian) through the lenses of contact, variation, and reconstruction, in an interdisciplinary and intradisciplinary way. This reveals at the same time the multiplicity and the unity of our discipline(s), both by showing what kind of results the adoption of modern theories on "old" material can yield, and by underlining the centrality and complexity of the text in any research related to ancient languages.