With the size of electronic devices approaching the nanometer scale. transition to self-assembly in molecular electronics systems appears to be technologically the next step to pursue, Quantum conductors with an especially high potential for applications are organic polymers and carbon nanotubes. The latter are being considered for use as both nonlinear electronic devices and as connectors between molecular electronics devices and the "outside world". Depending on their internal structure and the nature of the electric contact to leads, these systems may exhibit fractional conductance quantization. (C) 2002 Elsevier Science B.V. All rights reserved.