The present invention provides apelin receptor (APLNR) modulators that bind to APLNR and methods of using the same. The invention includes APLNR modulators such as antibodies, or antigen-binding fragments thereof, which inhibit or attenuate APLNR-mediated signaling. The invention includes APLNR modulators such as antibodies, or antibody fusion proteins thereof, that activate APLNR-mediated signaling. According to certain embodiments of the invention, the antibodies or antigen-binding fragments or antibody fusion proteins are fully human antibodies that bind to human APLNR with high affinity. The APLNR modulators of the invention are useful for the treatment of diseases and disorders associated with APLNR signaling and/or APLNR cellular expression, such as cardiovascular diseases, angiogenesis diseases, metabolic diseases and fibrotic diseases.