This disclosure provides ASCT2-binding molecules, e.g., anti-ASCT2 antibodies, and antigen-binding fragments thereof, used in methods related to cancer stem cells, e.g., binding to a cancer stem cell. In certain aspects, the ASCT2-binding molecules are conjugated to cytotoxic drugs, e.g., ASCT2 antibody-drug conjugates. In certain aspects, the ASCT2-binding molecules bind specifically to cancer stem cells expressing ASCT2.