Field electron emission from diamond and related "lms has been a popular topic of both experimental and theoretical research since the beginning of 1990s. Because of their low surface electron a$nity, chemical inertness and high thermal conductivity, this type of "lms is considered a strong candidate for cold-cathode materials. The "eld-emission properties of various types of diamond "lm are reviewed, and the milestone developments are identi"ed. Current theoretical models are compared. Potential applications of the diamond based cold-cathode emitters are predicted.