For decades, the Boeing 737 has been one of the defining aircraft in the short-haul markets, but its operational importance is best understood by the airlines that have built entire network strategies around the type. From Southwest Airlines’ single-type operating model to Ryanair’s ultra-low-cost expansion across Europe, the aircraft has proven itself as a key workhorse for low-cost operators. At the same time, the plane has proven it can be valuable for full-service network carriers as well.