The null subject has always been central to linguistic theory, because it tells us a great deal about the underlying structure of language in the human brain, and about the interface between syntax and semantics. Null subjects exist in languages such as Italian, Chinese, Russian and Greek where the subject of a sentence can be tacitly implied, and is understood from the context. In this systematic overview of null subjects, José A. Camacho reviews the key notions of null subject analyses over the past thirty years and encompasses the most recent findings and developments. He examines a balance of data on a range of languages with null subjects and also explores how adults and children acquire the properties of null subjects. This book provides an accessible and original account of null subject phenomena, ideal for graduate students and academic researchers interested in syntax, semantics and language typology.