With the continual improvements in optical technology it is essential that a measurement programme not only serves to satisfy the transmission performance requirements but also provides sufficient data to provide feedback for cable manufacturing and system design needs. A fibre optic transmission system consists of the electro optic interface, the optical cable link and the opto electric interface. Demountable optical connectors are normally fitted between the component parts of the system. The optical cable link is constructed from factory lengths, currently up to 2km, of multifibre cable field jointed to form a cable section of up to 50km in length. The cable section is then fitted with connectorised terminating units for interface to the terminal line equipment. This paper will discuss measurements on the cable only part of the fibre optic transmission system, that is measurement up to and between the optical connectors. Both multimode and single mode systems are discussed and the differences highlighted.