This collection of peer reviewed papers represents a concise, up-to-date summary of our current knowledge of planetary boundary layer (PBL) physics and parameterization. As such, it makes a major contribution to the interchange of knowledge and ideas between physicists, meteorologists and environmental modellers and sets out the course to be followed in subsequent research to improve PBL parameterizations in climate, numerical weather prediction, air quality, and emergency preparedness models. Major themes covered are: Nature and theory of turbulent boundary layers; Boundary layer flows modelling and applications to environmental security; Nature, theory and modelling of boundary-layer flows; and Air flows within and above urban and other complex canopies air-sea-ice interactions. The NATO Advanced Research Workshop, held in Dubrovnik, Croatia, 18-22 April 2006, that gave rise to this, book was attended by 57 scientists drawn from 21 countries on four continents. In recognition of his outstanding career and reaching the milestone age of 70, the workshop was dedicated to Professor Sergej Zilitinkevitch and a substantial number of contributions are based on or linked to his fundamental work.