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.Further, the possibilities of down-sizing the SCR catalyst are illustrated through the use of an ammonia slip catalyst or by improving the urea dosing control strategy. The impact of various dosing strategies is also shown using comparative tests on the same system.Another aspect of considerable importance is thermal management and the insulation of the after-treatment system, which is illustrated with experimental data.Finally, the importance of the studied areas for future legislations is discussed.