Nanofluidic systems and the studies on the behavior of liquids confined in nanometer-sized space are reviewed. Miniaturized chemical systems having nanometer-sized structures are fabricated by using advanced nanofabrication techniques. The size-confinement effect is expected to be applied in well-controlled chemical and biochemical analysis. While electroosmosis and electrokinetic migration in small-sized channels have been investigated extensively, there have been few reports on pressure-driven flow systems having nanometer-sized structures, which are widely used in laboratory-scale and micrometer-sized systems. In this review, fundamental technologies that can be used in integrated chemical analysis systems having nanometer-sized structures are introduced. In addition to the technological investigations, important topics in the fundamental research on the properties of liquids confined in nanometer-sized space are also presented.