A process for purification of a crude product stream recovered from the production of an unsaturated carboxylic acid by an aldolization reaction is disclosed. The product stream comprises the unsaturated carboxylic acid, aldehyde, saturated carboxylic acid, water, non-condensable vapours and optionally heavy by-products. The process comprises: providing the crude product stream in the vapour phase to a first separation column operated at a temperature and pressure to form an intermediate product stream comprising product unsaturated carboxylic acid, a portion of the water from the feed stream, a portion of the saturated carboxylic acid and heavy by-products where present; and passing the intermediate product stream to a second separation column operated at a temperature and pressure such that the unsaturated carboxylic acid product is separated and recovered.