Turbulent flow means fluid flow in which the fluid undergoes irregular fluctuations. Understanding the turbulent behaviour in flowing fluids is one of the most intriguing and important problems that have been the focus of research for decades due to its great importance in a variety of engineering applications. Common examples of turbulent flow include atmospheric and ocean currents, flow through turbines and pumps, blood flow in arteries, oil transport in pipelines, lava flow, and the flow in boat wakes and around aircraft wing tips, etc. In the present book, we focus on areas of current turbulence research. Recent progress on modelling and analysis of turbulent flows is reviewed, and likely directions for future research on these topics are indicated. This text is unusual in as much as it provides both general commentaries as well as recent specialized developments in the field of turbulence modelling.