The anomalous transport properties of the charge-density-wave system niobium triselenide are surveyed. Early experiments on the frequency dependence and non-ohmicity of the electrical conductivity are described together with interpretations using the sliding mode mechanism. The effect of impurities, the non-ohmic Hall effect, conduction noise, and ac conduction are described. Theoretical models which have been proposed arc discussed, together with difficulties from the experimental viewpoint. Lastly, mention is made of recent experiments on NbSe3 as well as other similar systems.