A method of manufacturing a three-dimensional object by additive layer manufacturing, comprising the following steps: - successively providing a plurality of layers (20a, 20b, 20c) of material in powder form, one on top of the other, on a support means inside a chamber, and - irradiating each layer with a laser beam or particle beam prior to providing the subsequent layer, wherein each layer is irradiated selectively only in those portions of the layer corresponding to the three-dimensional object being manufactured and wherein the irradiation is carried out in such a manner that the material is melted or sintered locally in the corresponding portions, wherein a gas atmosphere having a controlled pressure and composition is maintained inside the chamber at least during each of the irradiation steps, characterized in that - at least one of the pressure and the composition of the gas atmosphere inside the chamber is controlled such that at least two different gas atmospheres having different predetermined pressures and/or compositions are present inside the chamber during the irradiation of different ones of the layers, and - the temperature of the gas atmosphere inside the chamber is controlled such that at least two different temperatures of the gas atmosphere are present during the irradiation of different ones of the layers, and/or - the temperature of the layer being irradiated is controlled such that the temperature of the layers is changed between the irradiation of one or more pairs of adjacent layers such that at least two different temperatures of the layer being irradiated are present during the irradiation of different ones of the layers. - successively providing a plurality of layers (20a, 20b, 20c) of material in powder form, one on top of the other, on a support means inside a chamber, and - irradiating each layer with a laser beam or particle beam prior to providing the subsequent layer, wherein each layer is irradiated selectively only in those portions of the layer corresponding to the three-dimensional object being manufactured and wherein the irradiation is carried out in such a manner that the material is melted or sintered locally in the corresponding portions, wherein a gas atmosphere having a controlled pressure and composition is maintained inside the chamber at least during each of the irradiation steps, - at least one of the pressure and the composition of the gas atmosphere inside the chamber is controlled such that at least two different gas atmospheres having different predetermined pressures and/or compositions are present inside the chamber during the irradiation of different ones of the layers, and - the temperature of the gas atmosphere inside the chamber is controlled such that at least two different temperatures of the gas atmosphere are present during the irradiation of different ones of the layers, and/or - the temperature of the layer being irradiated is controlled such that the temperature of the layers is changed between the irradiation of one or more pairs of adjacent layers such that at least two different temperatures of the layer being irradiated are present during the irradiation of different ones of the layers.