An aqueous coating composition (especially a paint or varnish for buildings, vehicles, furniture and metal or plastics containers) which can form coatings on surfaces at ambient temperatures which on drying have improved early hardness and tack-resistance. The coating composition comprises water, optionally pigment and other conventional ingredients and dispersed particles of a highly non-crystalline polyester containing repeating hydroxyalkanoate units (preferably 3-hydroxybutyrate or 3-hydroxyvalerate or their copolymers). The polyester is non-crystalline to the extent that at least 60 wt % of the particles have a density of less than 102 % of Dmin where Dmin is the minimum density attainable by the polyester. The composition may also contain conventional film-forming polymers of the types used in aqueous paint or varnish.