The non renewable nature of petroleum products, its high cost together with high amount of atmospheric pollution caused by it has been a major concern in automobile industry. Thus the need to conserve this non renewable petrol and yet meet the needs of booming automobile industry led to the birth of a new advanced engine -Lean Burn Spark Ignition Engine. The ratio of air to fuel in a spark ignition engine is on average 14.7:1. With the diminishing oil reserves and tightened legislations, fuel consumption and exhaust emission of spark ignition engines is to be reduced. The efficiency of lean burn engines is high due to the usage of higher air fuel ratio. Lean burn engine can reach unburned hydrocarbon and carbon monoxide emission targets. The design features of lean burn engines can be improved with increased compression ratio, mixture swirl, mixture preparation, and improved ignition. As engine operates at leaner fuel levels, nitrogen emissions increase. Therefore, for lean burn engines to replace traditional fuel mixture engines, nitrogen oxide emission must be reduced. This can be done by catalyst or exhaust recirculation in the engine. However research continues to make lean burn engines ecologically viable.