Over the past decade the wireless industry increased capacity a thousandfold, and by doing fueled the explosive growth of mobile communication applications. Three key factors contributed to this huge capacity expansion: the dramatic improvement of spectral efficiency in 3G and 4G air interfaces, the unprecedented spectrum allocation for mobile networks in the world, and the continuing evolution of the radio access network and core network architecture. This paper describes the pivotal role of wireless protocol stack design behind these three factors that enabled and supported the evolution from 3G to 4G networks.