From one of the architects of the new science of simplicity and complexity comes a highly personal, unifying vision of the natural world. As a theoretical physicist, Murray Gell-Mann has explored nature at its most fundamental level. His achievements include the 1969 Nobel Prize for work leading up to his discovery of the quark - the basic building block of all atomic nuclei throughout the universe. But Gell-Mann is a man of many intellectual passions, with lifelong interests in fields that seek to understand existence at its most complex: natural history, biological evolution, the history of language, and the study of creative thinking. These seemingly disparate pursuits come together in Gell-Mann's current work at the Santa Fe Institute, where scientists are investigating the similarities and differences among complex adaptive systems - systems that learn or evolve by utilizing acquired information. They include a child learning his or her native language, a strain of bacteria becoming resistant to an antibiotic, the scientific community testing new theories, or an artist implementing a creative idea. The Quark and the Jaguar is Gell-Mann's own story of finding the connections between the basic laws of physics and the complexity and diversity of the natural world. The simple: a quark inside an atom. The complex: a jaguar prowling its jungle territory in the night. Exploring the relationship between them becomes a series of exciting intellectual adventures.