The paper will discuss the design and development of heavy-duty diesel engines to meet the US EPA 2010 on-highway standards - 0.2 g/HP-hr NOx and 0.01 g/HP-hr particulate matter (PM). In meeting these standards a combination of in-cylinder control and aftertreatment control for both NOx and particulate has been used.For NOx control, a combination of cooled exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) is used. The SCR catalyst uses copper zeolite to achieve high levels of NOx conversion efficiency with minimal ammonia slip and unparalleled thermal durability.For particulate control, a diesel particulate filter (DPF) with upstream oxidation catalyst (DOC) is used. While the DPF may be actively regenerated when required, it operates predominantly with passive regeneration - enabled by the high NOx levels between the engine and the DPF, associated with high efficiency SCR systems and NO₂ production across the DOC.The engine features a proprietary high pressure common rail fuel system (HPCR), developed jointly by Cummins and Scania. This HPCR system was developed for medium- and heavy-duty engines and is known as XPI. The XPI system was developed for very high pressure injection required by heavy-duty engines at US EPA 2010, EURO 5 and EURO 6 exhaust emission levels. Together with the variable geometry turbocharger (VGT), the HPCR provides flexibility for thermal management of the aftertreatment system. Thermal management is used extensively to provide fast warm-up and optimum DPF and SCR performance in use.This system architecture is designed to minimize both fuel and DEF consumption characteristics. With the adoption of copper zeolite SCR, it has been possible to achieve the near-zero US EPA 2010 emission standards, while reducing overall operating costs significantly (4-5%) when compared with the EPA 2007 engine it replaces.On-board diagnostics (OBD) has been fully implemented in these HD engines for 2010. This has required that all emission control systems be monitored for performance against emission thresholds, and that all related actuators and sensors be monitored for correct functionality.