Dynamic Modeling Demonstrates Good Correlation with Engine Measurement for Reduced Development Time: Recent and future exhaust emissions and fuel economy regulations have forced engine designers to use various engine and aftertreatment control devices to comply with the regulatory requirements. Consequently, the control system has become increasingly complex and engine development has become time-consuming and costly. The calibration task for cold-start emissions reduction especially needs to be more robust so that the emissions compliance is achieved while commercial value is sustained. Model-based calibration (MBC) was developed to reduce development time at Toyota. The model has been used for calibration of the engine control system for basic operations and in modeling engine operations under steady-state conditions. However, MBC has not been applied to the calibration process for cold-start operation under transient conditions. This chapter reports the development approach, techniques, validation, and exhaust emissions measurement results.