Definiteness has been a central topic in theoretical semantics since its modern foundation. However, despite its significance, there has been surprisingly scarce research on its cross-linguistic expression. With the purpose of contributing to filling this gap, the present volume gathers thirteen studies exploiting insights from formal semantics and syntax, typological and language specific studies, and, crucially, semantic fieldwork and cross-linguistic semantics, in order to address the expression and interpretation of definiteness in a diverse group of languages, most of them understudied. The papers presented in this volume aim to establish a dialogue between theory and data in order to answer the following questions: What formal strategies do natural languages employ to encode definiteness? What are the possible meanings associated to this notion across languages? Are there different types of definite reference? Which other functions (besides marking definite reference) are associated with definite descriptions? Each of the papers contained in this volume addresses at least one of these questions and, in doing so, they aim to enrich our understanding of definiteness.