This invention relates generally to the generation of antibodies, e.g., monoclonal antibodies including fully human monoclonal antibodies, that recognize Jagged 1 and/or Jagged 2, to antibodies, e.g., monoclonal antibodies including fully human antibodies that recognize Jagged 1 and/or Jagged 2, and nucleic acid molecules that encode antibodies, e.g., nucleic acid molecules that encode monoclonal antibodies including fully human cross-reactive antibodies that recognize both Jagged 1 and Jagged 2, and to methods of making the anti-Jagged antibodies and methods of using the anti-Jagged antibodies as therapeutics, prophylactics, and diagnostics. The invention also relates generally to activatable antibodies that include a masking moiety (MM), a cleavable moiety (CM), and an antibody (AB) that specifically bind to Jagged 1 and Jagged 2, and to methods of making and using these activatable anti-Jagged antibodies in a variety of therapeutic, diagnostic and prophylactic indications.