Molecularly small confined phases play an important role in many scientific and engineering disciplines. For instance, the confining membrane of a living cell is known to affect the structure and transport of cellular water, which mediates the cell's metabolism and other biochemical processes. Transport of hazardous waste through the soil is strongly influenced by the adsorption of bulk phase molecules on the confining mineral _surfaces. Finally, molecularly thin confined fluid films play a prominent part in lubrication. These examples illustrate the broad range of natural and commercial processes to which the present subject pertains. Much experimental effort has been devoted to molecularly small confined phases, revealing the intriguing nature of such systems. Several sections of this book are therefore devoted to descriptions of experimental techniques. To date even the most refined experiments do not yield direct information about structure and processes on the molecular scale. Computer simulations, on the other hand, do give such information and therefore complement real laboratory experiments. Several sections of this book discuss the link between experiments and the corre­ sponding simulations.