Much recent research investigates children's understanding of the sources of human knowledge and the relation of this understanding to socio-cognitive development. This volume highlights new research in this area that focuses on evidentials: word affixes and sentence particles that indicate the speaker's source of knowledge--for example, perception, inference, or hearsay. Evidentials are a feature of about a quarter of the languages in the world and have a variety of interesting characteristics. For examples, in contrast to lexical alternatives familiar from English, such as "I saw," they are extremely frequent. The volume brings together scholars pioneering research on evidentiality in Bulgarian, Japanese, Tibetan, and Turkish. Their contributions to this volume provide a glimpse at the diversity of evidential systems around the globe while examining a number of provocative questions: OL {list-style:disc} P:{margin-left 60px} * How do evidentials mediate children's acquisition of knowledge from others' testimony? * What is the relation between grammaticalized and lexical expressions of source of knowledge? * Does the acquisition of an evidential system boost source monitoring and inferential skills? The volume is a compelling illustration of the relevance of evidentiality to broadening our understanding of development in many domains, including theory of mind, memory, and knowledge acquisition. This is the 125th volume of the Jossey-Bass quarterly report series New Directions for Child and Adolescent Development. The mission of this series is to provide scientific and scholarly presentations on cutting edge issues and concepts in the field of child and adolescent development. Each volume focuses on a specific new direction or research topic, and is edited by an expert or experts on that topic.