The Handbook of Weather, Climate, and Water provides an authoritative report at the start of the 21St Century on the state of scientific knowledge in these exciting and important earth sciences. Weather, climate, and water affect every person on earth every day in some way. These effects range from disasters like killer storms and floods, to large economic effects on energy or agriculture, to health effects such as asthma or heat stress, to daily weather changes that affect air travel, construction, fishing fleets, farmers, and mothers selecting the clothes their children will wear that day, to countless other subjects. During the past two decades a series of environmental events involving weather, climate, and water around the globe have been highly publicized in the press: the Ozone Hole, Acid Rain, Global Climate Change, El Ninos, major floods in Bangladesh, droughts in the Sahara, and severe storms such as hurricane Andrew in Florida and the F5 tornado in Oklahoma. These events have generated much public interest and controversy regarding the appropriate public policies to deal with them. Such decisions depend critically upon scientific knowledge in the fields of weather, climate, and water.