Volume 1: http://Photos.com: 3, 17, 37, 57, 62, 66, 70, 77, 96, 103, 107, 114, 119, 128, 137, 149, 162, 170, 177, 202, 211, 228, 234, 245, 251, 258, 297, 304, 305, 313, 334, 363, 390, 398, 409, 416, 427, 432, 453, 466, 476, 484, 499, 502, 508, 515, 522, 527, 542, 549, 554, 562; iStockphoto: 48, 197, 325, 459, 537; USAID: 8 (Mina Luka); New York Department of Sanitation Museum Project: 280; StockXchange: 23; Wikimedia Commons: 26, 43, 51, 92, 139, 186, 191, 218, 223, 263 (Alan Stanton), 273, 339, 357, 423, 441 (Elgaland Vargaland), 495 (William Wesen), 571; Public Domain via Wikimedia: 318; Project Gutenberg via Wikimedia: 352; U.S. Department of Energy: 345; U.S. Army Signal Corps: 383.

Volume 2: http://Photos.com: 578, 585, 595, 602, 612, 621, 629, 636, 648, 657, 666, 578, 585, 595, 602, 612, 621, 629, 636, 648, 657, 666, 680, 691, 701, 732, 739, 747, 769, 776, 784, 793, 806, 815, 831, 841, 849, 876, 893, 899, 907, 916, 924, 935, 947, 957, 963, 985, 1006; Wikimedia: 868 (Lawrence Fung), 875; NASA: 857; World Bank: 673, 759; iStockphoto: 710, 724, 823, 885; Walton County Florida Government: 979; Environmental Protection Agency: 972.