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The Euro IV legislation for heavy-duty on-road vehicles enforces emissions limits on the tailpipe NOx levels during both transient and modal testing, typically paired with additional limitations on, for example, ammonia emissions. There are several possible strategies for complying with the legislation, including engine management measures as well as after-treatment in the form of catalytic removal of NOx with ammonia as the reducing agent. Based on experimental data, a range of important aspects are presented and discussed, with both overall system performance and the installation and operational costs in mind. Factors relevant for future legislations, in the form of EU V and beyond, are also discussed. Operating the engine with high levels of Exhaust Gas Recirculation (EGR) is a possible path to EU IV compliance with no or little catalytic NOx reducing after-treatment. Here, it is contrasted against an SCR-only solution based on a non-EGR engine calibration.