Abstract: The invention relates to an improvement in a process for the production of carbon fibres (also filaments and films) from organic material consisting mainly of hydrocarbons (e.g., pitch, tars, solutions or extracts of coal). The organic material is spun or extruded to form a fibre, oxidized to stabilize it to heat treatment and subsequently carbonized. The invention comprises employing in place of, or as, the organic material consisting mainly of hydrocarbons a modified organic material formed by reacting an aromatic hydrocarbon material having at least two fused rings (which may be such an organic material consisting mainly of hydrocarbons) with a cross-linking agent, the cross-linking agent having at least two groups selected from groups that react with and substitute onto aromatic hydrocarbon rings. Suitable groups include acyl chloride, alkyl chloride, carboxylic acid anhydride, olefin, and alcoholic hydroxyl groups.