An apparatus for generating control data for production of a three-dimensional object, comprising: an interface arranged to receive: object data for a three-dimensional object to be generated, and selection data indicating at least one build material to be used to generate the three-dimensional object, the at least one build material being coalescable by the application of energy to a coalescing agent applied to the build material; and a controller (220, 410) arranged to access build material profile data for the at least one build material indicated in the selection data, wherein build material profile data for a given build material defines one or more parameter values that are dependent on the properties of the given build material and that are configured to generate a three-dimensional object with predefined build properties, and wherein at least one parameter value relates to an interaction of a coalescence modifier agent and the given build material, the coalescence modifier agent acting to modify the effects of the coalescing agent and being used to modify coalescence of the given build material in the production of the three-dimensional object, the controller (220, 410) being arranged to generate control data (280, 415) for the production of a three-dimensional object by applying the accessed build material profile data to the received object data. an interface arranged to receive: object data for a three-dimensional object to be generated, and selection data indicating at least one build material to be used to generate the three-dimensional object, the at least one build material being coalescable by the application of energy to a coalescing agent applied to the build material; and object data for a three-dimensional object to be generated, and selection data indicating at least one build material to be used to generate the three-dimensional object, the at least one build material being coalescable by the application of energy to a coalescing agent applied to the build material; and a controller (220, 410) arranged to access build material profile data for the at least one build material indicated in the selection data, wherein build material profile data for a given build material defines one or more parameter values that are dependent on the properties of the given build material and that are configured to generate a three-dimensional object with predefined build properties, and wherein at least one parameter value relates to an interaction of a coalescence modifier agent and the given build material, the coalescence modifier agent acting to modify the effects of the coalescing agent and being used to modify coalescence of the given build material in the production of the three-dimensional object, wherein build material profile data for a given build material defines one or more parameter values that are dependent on the properties of the given build material and that are configured to generate a three-dimensional object with predefined build properties, and wherein at least one parameter value relates to an interaction of a coalescence modifier agent and the given build material, the coalescence modifier agent acting to modify the effects of the coalescing agent and being used to modify coalescence of the given build material in the production of the three-dimensional object, the controller (220, 410) being arranged to generate control data (280, 415) for the production of a three-dimensional object by applying the accessed build material profile data to the received object data.