  The electrical transport properties of atomic-scale conductors are reviewed,
with an emphasis on the relations of this problem with studies on quantum size
effects in metallic clusters. A brief introduction is given of the natural
formalism for discussing electron transport in ballistic conductors: the
Landauer theory. After introducing the experimental techniques, which are used
for studying ballistic point contacts in metals, the experimental observations
for the conductance of atomic-scale contacts are presented. In order to obtain
a full description in terms of the quantum modes for conductance, several
recently developed techniques are reviewed, which go beyond straightforward
measurement of the conductance. A brief discussion is given of an unusual
atomic geometry for gold contacts, which evolve into a chain of freely
suspended atoms. Then shell filling effects in sodium nanowires are discussed
in the context of the influence of the conductance modes on the total energy of
the system. The chapter ends with an outlook on promising new developments.
