In the past quarter-century, charter schools have grown from a ragtag insurgency into a serious force in American K-12 education, serving as the public education provider for nearly three million children across the country. But this nationwide growth has spread unevenly across U.S. cities. In most places, urban districts have successfully contained the charter insurgents, keeping them marginal and maintaining district preeminence--if not hegemony. In a small but growing number of cities, however, the charter sector has thrived and become a more serious contender for market share and educational power, too large for the prevailing power to ignore. "Engagement" of some kind has become necessary. But what form does that engagement take? To find out, this report examines district-charter engagement in five cities--Boston, Cleveland, Denver, Houston, and Washington, D.C.--in pursuit of three questions: (1) How are districts engaging charters? (2) Why do districts choose to engage charters? and (3) Is engagement resulting in improvement? [Foreword by Amber N. Northern and Michael J. Petrilli.]