The present invention provides antibodies which bind to the Delta/Serrate/LAG-2 consensus sequence (DSL) domain of human Jagged 1 via novel epitopes comprising the residue E228, and inhibit the interaction between human Jagged 1 and its associated receptors. Said antibodies may be administered therapeutically in the treatment of tumors/cancer, preferably those associated with tumoral Jagged 1-mediated signalling and tumor microenvironmental processes in which Jagged 1 and/or Notch-mediated signalling has been implicated, including those comprising Jagged 1-mediated cross talk between the tumor and the tumor microenvironment. The present invention also provides pharmaceutical compositions comprising said antibodies, uses of said antibodies in therapy, hybridomas comprising and/or secreting said antibodies and cells or cell lines expressing said antibodies and humanized/deimmunized variants in recombinant form.