The 2.7 billion people living on $2 a day (or less) are not just the world's greatest challenge, they represent an extraordinary market opportunity. By learning how to serve them ethically and effectively, businesses can earn handsome profits while helping to solve one of the world's most intractable problems. The authors show how Zero-Based Design can enable unapologetic capitalists to supply the very poor with clean drinking water, electricity, irrigation, housing, education, healthcare, and other necessities at a fraction of the usual cost and at profit margins attractive to investors.