Methane plays many important roles in the earth's environment. It is a potent "greenhouse gas" that warms the earth; controls the oxidizing capacity of the atmosphere (OH) indirectly affecting the cycles and abundances of many atmospheric trace gases; provides water vapor to the stratosphere; scavenges chlorine atoms from the stratosphere, terminating the catalytic ozone destruction by chlorine atoms, including the chlorine released from the man-made chlorofluorocarbons; produces ozone, CO, and CO2 in the troposphere; and it is an index of life on earth and so is present in greater quantities during warm interglacial epochs and dwindles to low levels during the cold of ice ages. By all measures, methane is the second only to CO2 in causing future global warming. The book presents a comprehensive account of the current understanding of atmospheric methane, and it is an end point for summarizing more than a decade of intensive research on the global sources, sinks, concentrations, and environmental role of methane.