In this thesis I will describe the conductance properties of certain organic molecules.

I will first show that two metal electrodes can be fabricated with a nm-scale gap between them by causing electomigration-induced failure in a nanoscale wire. These two electrodes are separated by a few nanometers from a metallic gate electrode. Organic molecules can be incorporated into the gap between the electrodes creating a transistor geometry.

Transport measurements on metal-organic complexes at low temperatures show Coulomb blockade and Kondo-assisted tunneling. Using the specially designed molecule C$_{140}$, I have studied the coupling between the vibrational modes of the molecule and electron flow through transistors made from it.

I have also been able to make magnetic electrodes to pass spin-polarized current through molecules. Using this, I have studied the coexistence of the Kondo effect and ferromagnetism in the electrodes.

I have also modified the technique to have a mechanically adjustable distance between the two electrodes, which is useful for studying the influence of the contact on the conductance of a device.