This chapter focuses on the development of concepts that children draw on as they work toward understanding negative numbers. Framed from a conceptual change lens, I discuss different interpretations children have of minus signs, numerical order, numerical values, and addition and subtraction operations and how children draw on these varied conceptions to solve addition and subtraction problems involving negative numbers. Children's unconventional attempts at solving these problems reflect their efforts to make sense of negatives in light of their whole number understanding. [For the complete volume, "Constructing Number: Merging Perspectives from Psychology and Mathematics Education. Research in Mathematics Education," see ED616587.]