Dennis Lamb is Professor Emeritus of Meteorology at Pennsylvania State University. Professor Lamb worked as a researcher for nearly fourteen years at the Desert Research Institute (Reno) before embarking on a teaching career at Pennsylvania State University. With more than forty years of observational and laboratory research experience and more than twenty years teaching cloud physics and atmospheric chemistry at both undergraduate and graduate levels, he now realizes that the best path toward understanding clouds is to understand water itself, at the molecular level. The deeper the understanding, the greater becomes the appreciation of clouds as gate keepers in the water cycle and energy budget of Earth. This book is the culmination of his career studying the physics and chemistry of water and clouds. Hans Verlinde is a Professor of Meteorology at Pennsylvania State University. He is an observational meteorologist who has studied clouds in the Antarctic, at the equator and in the Arctic. He is currently the site scientist for the US Department of Energy Atmospheric Radiation Measurement Program Climate Research Facility at Barrow on the North Slope of Alaska, and he teaches classes in atmospheric thermodynamics, cloud physics, mesoscale meteorology and radar meteorology at Pennsylvania State University.