BS IV or Bharat Stage are emission standards that are set by the Government of India, these norms regulate the output of pollutant car engines. These stringent norms are based on the European regulations since 2000. All the car manufacturers have to comply with these regulations in order to get a go certificate from the regulating authority for their car. India 2000 (2000), Bharat Stage II (2003), Bharat Stage III (2005) and at present Bharat Stage IV (2010) norms are placed in more than 20 major cities across India and Bharat Stage V on the way.
You might already be aware of the production being stopped for the iconic Maruti 800, this was due to Maruti not willing to comply with the recent Bharat Stage norms, so was the end of life for the 2-stroke engines and also the inclusion of many electronic controls in modern day cars. The emission norms are good in the way that they help bring down the pollution levels but at one place they’re bad is the cost factor, they increase the cost of the car due to the added advancements and high fuel prices.
Some car manufacturers who weren’t willing to comply with the Bharat Stage IV norms resulted in some of their non-complying cars being denied license. Maruti 800,Hyundai Getz, Skoda Fabia and Octavia, Fiat Palio, Tata Sumo Victa and Indica V2, Chevrolet Tavera, Ford Ikon, Mitsubishi Lance and Pajero and Hindustan Ambassador.
Now with Bharat Stage V in the pipelines, it will only be implemented once the Bharat Stage V fuel is available on a pan-India basis.