No comprehensive volume of scholarly studies has ever been devoted entirely to De signis/On Signs, a work of considerable importance by the Epicurean philosopher Philodemus of Gadara (1st century BCE) partially preserved in the Herculaneum library (PHerc. 1065). The present collection of multilingual essays seeks to fill this gap. De signis is one of the most important texts for reconstructing the Hellenistic debate between Epicureans and Stoics concerning inference from signs. It is a document of exceptional importance for the reconstruction of the history of Epicureanism and its doctrinal developments too, and above all, for a detailed understanding of crucial aspects of both Epicurean and Stoic epistemology and theories of language. A serious historical-philosophical reconstruction of Hellenistic epistemologies cannot afford to overlook this work by Philodemus. The present volume is organised into four parts. Part I (Papyrological and Literary Aspects) examines Philodemus’ treatise from both papyrological and philological-literary perspectives. Part II (Sign-Inference) explores the theoretical core of De signis: inference from signs. Part III (Key Concepts and Specific Topics) scrutinises some of the fundamental concepts in De signis, alongside specific topics addressed in the treatise that help to further clarify its challenging columns. Part IV (Historical Context and Reception) addresses the historical and cultural context to which De signis belongs, as well as its ancient and modern reception (for instance, by Charles S. Peirce).