Abstract: An electronic seal (2) is disclosed which comprises a housing (4,104) and a closure member co-operable with the housing to form a seal. The closure member may for example take the form of an elongate member (6, 106) connectable at both of its ends to the housing. The closure comprises an outer portion (8, 108) surrounding a core (10, 10A, 110). A sensor assembly (14, 16, 135, 136) is provided for sensing integrity of the core. Hence tampering with the seal can be detected. The core may be formed as a fiber optic cable (10, 10A with an integrity sensor comprising an optical source 14 and an optical detector 16.