The present invention provides antibodies and related molecules that bind to chemokine receptor 4 (CXCR4). The invention further provides antibody-drug conjugates comprising such antibodies, antibody encoding nucleic acids, and methods of obtaining such antibodies. The invention further relates to therapeutic methods for use of these antibodies and anti-CXCR4 antibody-drug conjugates for the treatment of a disorder associated with CXCR4 function or expression (e.g., cancer), such as colon, RCC, esophageal, gastric, head and neck, lung, ovarian, pancreatic cancer or hematological cancers.