Why is the fuel economy of Audi vehicles better than other brands?

I'm looking to buy a new car and have heard that Audi vehicles have a better fuel economy compared to other luxury brands. Can anyone explain why this is the case and what factors contribute to their efficiency?

According to Audi, their vehicles are designed with lightweight, aerodynamic bodies and efficient engines to maximize fuel economy. They also offer advanced technologies such as start-stop systems and regenerative braking to further increase efficiency.