Recent developments in micro- and nanotechnologies made possible the fabrication of devices integrating a deterministic network of nanochannels, i.e., with at least one dimension in a range from 1 to 100 nm. The proximity of this dimension and the Debye length, the size of biomolecules such as DNA or proteins, or even the slip length, added to the excellent control on the geometry gives unique features to nanofluidic devices. This new class of devices not only finds applications wherever less well-defined porous media, such as electrophoresis gels, have been traditionally used but also give a new insight into the sieving mechanisms of biomolecules and the fluid flow at the nanoscale. Beyond this, the control on the geometry allows smarter design resulting, among others, in new separation principles by taking advantage of the anisotropy. This perspective gives an overview on the fabrication technologies of nanofluidic devices and their applications. In the first part, the current state of the art of nanofluidic fabrication is presented. The second part first discusses the key transport phenomena in nanochannels. Current applications of nanofluidic devices are next discussed. Finally, future challenges and possible applications are highlighted.