The collection of studies in this special issue make an important contribution to our understanding and measurement of the core cognitive and noncognitive factors that influence children's emerging quantitative competencies. The studies also illustrate how the field has matured, from a time when the quantitative competencies of infants and young children were studied in isolation of other cognitive abilities or social contexts. The studies illustrate how the basic knowledge gleaned from this early research can now be situated within the home environment, integrated with language development, and as related to children's preparation for learning formal mathematics in school.