Children acquiring two languages, either simultaneously or sequentially, have more variation in their linguistic input than their monolingual peers. Understanding the nature and consequences of this variability has been the focus of much recent research on childhood bilingualism. This volume constitutes the first collection of research solely dedicated to the topic of input in childhood bilingualism. Chapters represent a range of theoretical and methodological approaches to the study of childhood bilingualism, covering a variety of language combinations and sociocultural contexts in Europe, Israel, North and South America.