The liquid state of matter is an intermediate phase between solid and gas. A liquid is a fluid. Unlike a solid, the molecules in a liquid have a much greater freedom to move. The forces that bind the molecules together in a solid are only temporary in a liquid, allowing a liquid to flow while a solid remains rigid. Like the particles of a solid, particles in a liquid are subject to intermolecular attraction; however, liquid particles have more space between them, so they are not fixed in position. The attraction between the particles in a liquid keeps the volume of the liquid constant. The movement of the particles causes the liquid to be variable in shape. Liquids will flow and fill the lowest portion of a container, taking on the shape of the container but not changing in volume. Liquid is one of the four primary states of matter, with the others being solid, gas and plasma. The limited amount of space between particles means that liquids have only very limited compressibility. This Book addresses modern problems in the fields of liquids, solutions and confined systems, critical phenomena, as well as colloidal and biological systems. The book focuses on state-of-the-art developments in contemporary physics of liquid matter structure of liquids in confined systems, phase transitions, supercritical liquids and glasses, and covers the most recent developments in the broader field of liquid state. Recent trends and progress in the field of liquid matter are explored in this volume by a wide spectrum of contributions from liquid state physicists, chemists and chemical engineers.