Armed forces are ever more likely to fight in cities as the world becomes increasingly urbanized. Accordingly, public and moral concerns about the costs of war borne by noncombatants increase as well. This report is a study of urban warfare and its challenges for U.S. armed forces constrained by having to minimize noncombatant casualties and collateral damage. America's armed forces are likely to have to confront the hell of urban combat. They have the potential to do so successfully. However, this environment's challenging character is unalterable; it will consume any force that fights unprepared. This study, based on an in-depth literature search and scores of interviews, has three primary objectives: (1) Describe the conditions confronting a ground force fighting under the constraints of minimizing noncombatant casualties and collateral damage, along with the difficulties of fighting under such conditions in urban areas; (2) Identify U.S. armed forces' current capabilities and ongoing efforts to enhance them; and (3) Determine current shortfalls and present potential remedies for identified vulnerabilities. Consideration of such solutions will include analysis of feasible changes in doctrine, training, and technologies that would give regular U.S. forces the capability to successfully perform constrained urban operations.