In the recent years, due to rising fuel costs, transportation technologies that provide better fuel economy than conventional vehicle are gaining in popularity with masses. Also, tighter emission norms by various governments have prompted OEMs to look at alternate solutions such as hybrid vehicles. Hybrid vehicles employ an internal combustion engine as well as an alternate energy source to power road vehicles. Various types of hybrid vehicles are available such as mild hybrid, full hybrid, series, parallel and series-parallel hybrids. The level of hybridization (mild or full) and the different powertrain combination (series or parallel) result that on the same route, the engine in a hybrid vehicle operates very different to that of conventional vehicle. The fuel consumed and emissions are also significantly lower in hybrid vehicle. To certify hybrid vehicles, regulators in many countries have modified existing procedures applicable to conventional vehicles. This paper gives an overview about the types of hybrid Powertrain combination. Indian procedure for certification of Heavy Duty Hybrid vehicles is explained. Other methods for emission testing being used worldwide are also presented here.