Recent advances in nanofluidic technologies have enabled devices to be fabricated that integrate nanochannels with at least one dimension smaller than several hundred nanometers. Since this dimension is close to the sizes of biomolecules such as DNA, proteins, and other biomolecules, it opens up new scientific and technological fields based on analysis and manipulation of single molecules. This paper reviews the current state of knowledge regarding single molecular level analysis and processing in nanochannels, particularly experimental findings in this area. While there have been many theoretical and molecular simulation studies, this paper surveys experimental studies. Following a brief survey of techniques for fabricating nanochannels, we review fundamental studies of single molecule behavior and manipulation in nanochannels. We then discuss important transport phenomena of single molecules in nanochannels. Finally, the emerging challenge of electrical single-molecule detection and its possible applications are highlighted.