According to one example, there is provided a system for generating a three-dimensional object. The system comprises a carriage to move bi-directionally along a first axis relative to a support platform. The carriage is to receive, or have installed thereon, a plurality of modules each to perform an operation from a set of operations to generate a layer of a three-dimensional object. The system further comprises a controller to cause relative movement between the carriage and the support platform along the first axis, and to control, during the relative movement, operation of the modules to perform the set of operations in a predefined order.