[en] ASSERT-4 is an advanced subchannel code being developed primarily to model single- and two-phase flow and heat transfer in horizontal rod bundles. This manual is intended to facilitate the application of this code to the analysis of flow in reactor fuel channels. It contains a brief description of the thermalhydraulic model and ASSERT-4 solution scheme, and other information required by users. This other information includes a detailed discussion of input data requirements, a sample problem and solution, and information describing how to access and run ASSERT-4 on the Chalk River computers