Details are given of an experimental study of field emission characteristics of diamond-coated Mo electrodes: in particular, a transparent anode imaging technique was used to monitor the spatial distribution of the individual emission centres. This study has revealed the important fact that substantial emission can be obtained at fields as low as 5 MV m-1. In order to investigate the physical nature of the emission process, a comparative study has been made of emission obtained from a diamond-coated electrode and a bulk carbon graphite electrode. Significantly, it was found that both the graphite-rich diamond film and the diamond-rich graphite electrode shared a similar highemissivity characteristic, with a high surface density of emission sites. It has also been noted that cvo diamond films have two important properties that are favourable to low-field cold electron emission, namely their negative electron affinity and the presence of graphite inclusions.