Modern high-energy accelerators used for high energy physics research have relied upon the generation of electromagnetic fields oscillating at radio frequencies (RF) to provide kinetic energy to charged particles. In this talk we will review the history of RF accelerators and discuss some of the issues facing the advancement of accelerators of ever-increasing size and complexity. Existing energy-frontier accelerators using standard RF technology demand innovative upgrades to continue to meet the requirements of the user community. As the Large Hadron Collider finally nears completion in Europe, and an International Linear Collider community attempts to form, these facilities, too, are designing toward upgradeability. A short glimpse of the LHC, the ILC concept, and possible future acceleration techniques will be provided.