Loaded with aerial plants and the millions of creatures dependent upon them, tropical tree crowns are the last and greatest ecological frontier. Hundreds of species - earthworms, frogs, lichens, flowers - never descend to earth during their lifetimes. Eight out of ten remain unnamed and unclassified by science. Donning rock-climbing gear to join researchers working 150 feet and more above the ground, Mark Moffett photographed strangler trees in Borneo, giant squirrels in India, and canopy bears in Colombia. He also entered the terrifying world of arboreal spiders and ants, photographing them under extreme magnification. Described as a world-roving zoologist by National Geographic magazine, Moffett has documented virtually every major active canopy research site. The immediacy of his writing and the intelligence of his photography make the canopy's fantastic architecture and unearthly inhabitants accessible to the general reader. In the tradition of the great 19th-century explorers, he captures the struggles of the individual scientists and the passions that enable them to brave perilous situations in pursuit of their work.