Why is the Audi A2 considered a fuel efficient vehicle?

I am interested in purchasing an Audi A2 and heard that it is known for its fuel efficiency. Can you provide some details on the technology and features that make it stand out in terms of fuel economy?

The Audi A2 incorporates advanced aerodynamics, lightweight materials, and an efficient engine to enhance its fuel economy. On average, it can achieve 37 miles per gallon.

The A2 also features a start-stop system that automatically turns off the engine when the car is at a standstill, reducing fuel consumption and emissions.