This commentary raises and discusses questions based on some of the agreements, disagreements, and themes found in the four chapters on fractions. It considers (1) the importance of tasks that are based in perception and readily available activity in light of an emphasis on problem solving in mathematics education, and the role that theories about thinking and learning play in designing such tasks; (2) some potential connections among various theories about thinking and learning as they relate to fractions; (3) the natural number bias and how ideas about natural numbers could serve as a foundation for fractions; and (4) the roles that magnitude, measurement, and linear representations of number play for fractions. [For the complete volume, "Constructing Number: Merging Perspectives from Psychology and Mathematics Education. Research in Mathematics Education," see ED616587.]