While often treated as separate entities, there is a significant interaction between engine operating parameters and the catalytic aftertreatment system in determining overall performance. The impressive gains in vehicle emissions and durability required for such marketplaces, as California and Europe provide excellent examples of this interrelationship. Similarly, the Indian marketplace can expect to follow these technology progressions in engine as well as catalyst application design. To progress from an unregulated emissions environment to the first level of catalyzed aftertreatment of relatively simply designed carbureted engines, and then to more sophisticated engines with fuel injection, India can take advantage of what has been learned in other marketplaces worldwide.Different automotive catalyst technologies process the emissions from an engine with different responses to variations in engine operating parameters of primary importance is the distinction between a purely oxidative aftertreatment in which unburned hydrocarbons (HCs) and CO can be effectively converted, and fully three-way emissions control requiring engine operation close to the A/F stoichiometric point under all conditions. This distinction has impact on both the choice of catalyst technology and the specific engine operating factors impacting and limiting typical conversion performance.Catalyst durability can be attributed to two types of deactivation mechanisms: (a) thermal deactivation, and (b) poisoning. Thermal deactivation is primarily caused by periods of very high temperature operation as a result of the oxidation of HCs and CO in high concentration. These conditions arise under certain vehicle operating modes. Two factors influence the extent of deactivation, the temperature level and the time spent at these temperatures. Poisoning arises through the deposition of foreign material onto the catalyst from either fuel or lubricant sources. Of particular concern is the extreme impact of even small amounts of residual lead in fuel as the inventory of leaded fuel is slowly purged from the fuel industry's infrastructure.