Economic development around the world has proceeded further than analysts half a century ago dared to hope. But development has not been universal, and the hardest cases -- states that lack social cohesion or are "fragile" -- remain underdeveloped. Conventional approaches to spurring development, through foreign aid, technical assistance, or exhortation by Western governments and nongovernmental organizations, have obviously failed in such places, where Western notions of a competently governed, democratic central state have often not taken hold. Kaplan, a business consultant, here reviews the reasons for these failures and offers ten guiding principles for altering conventional approaches to development, largely through much greater formal recognition of diverse cultural, linguistic, and tribal identities within state boundaries and through building both loyalty and accountability at the local level. He then offers suggestions based on these principles for dealing with seven difficult cases, each of which presents distinctive challenges and opportunities: western Africa, where a regional approach is espoused, the Democratic Republic of the Congo, Syria, Somaliland (Somalia as a whole is abandoned), Bolivia, Pakistan, and Azerbaijan. This is a stimulating contribution to a growing literature on how to deal with fragile states.