The disclosure provides binding proteins that bind CD38 polypeptides, e.g., human and cynomolgus monkey CD38 polypeptides. For example, the binding proteins can be monospecific, bispecific, or trispecific binding proteins with at least one antigen binding domain that binds a CD38 polypeptide. The disclosure also provides methods for making binding proteins that bind CD38 polypeptides and uses of such binding proteins.