Apparatus for generating a three-dimensional object, comprising: a first agent distributor to selectively deliver a coalescing agent onto portions of a layer of build material; a second agent distributor to selectively deliver a coalescence modifier agent onto portions of a layer of build material; an energy source to apply energy in a substantially uniform manner to the whole surface of a layer of build material such that upon temporary application of energy: build material on which coalescing agent is delivered heats up above the melting point of the build material, coalesces and solidifies upon cooling; and build material on which no coalescing agent is delivered does not heat up above the melting point and does not coalesce; and a controller to control the agent distributors to selectively deliver each of the agents onto a layer of build material in respective patterns derived from data representing a slice of a three-dimensional object to be generated, wherein the coalescence modifier agent is delivered adjacent to where the coalescing agent is delivered to help reduce the effect of lateral coalescence bleed, so that when energy is applied to the layer the build material coalesces and solidifies to form a slice of the three-dimensional object in accordance with the patterns. a first agent distributor to selectively deliver a coalescing agent onto portions of a layer of build material; a second agent distributor to selectively deliver a coalescence modifier agent onto portions of a layer of build material; an energy source to apply energy in a substantially uniform manner to the whole surface of a layer of build material such that upon temporary application of energy: build material on which coalescing agent is delivered heats up above the melting point of the build material, coalesces and solidifies upon cooling; and build material on which no coalescing agent is delivered does not heat up above the melting point and does not coalesce; and a controller to control the agent distributors to selectively deliver each of the agents onto a layer of build material in respective patterns derived from data representing a slice of a three-dimensional object to be generated, wherein the coalescence modifier agent is delivered adjacent to where the coalescing agent is delivered to help reduce the effect of lateral coalescence bleed, so that when energy is applied to the layer the build material coalesces and solidifies to form a slice of the three-dimensional object in accordance with the patterns. build material on which coalescing agent is delivered heats up above the melting point of the build material, coalesces and solidifies upon cooling; and build material on which no coalescing agent is delivered does not heat up above the melting point and does not coalesce; and a controller to control the agent distributors to selectively deliver each of the agents onto a layer of build material in respective patterns derived from data representing a slice of a three-dimensional object to be generated, wherein the coalescence modifier agent is delivered adjacent to where the coalescing agent is delivered to help reduce the effect of lateral coalescence bleed, so that when energy is applied to the layer the build material coalesces and solidifies to form a slice of the three-dimensional object in accordance with the patterns.