The dynamics wetting of fiber is of crucial importance in the fields, such as composites, optical fiber or textile industries. It is therefore valuable to acquire a clear understanding of the fundamental physical mechanisms which govern this phenomenon. A new theoretical approach is proposed and validated both by experiments and molecular dynamics simulations. The experiments consist in capturing images of meniscus formation around the fiber via a high speed camera. The same kind of procedure is followed to study the spontaneous spreading and the forced wetting of a nanofiber by simulations. It is confirmed that for a given equilibrium contact angle, a maximum of speed wetting occurs. Moreover, a comparison between the values of the microscopic parameters obtained via the adjustement of the theory and a direct measurement of these parameters permits us to check the validity of the chosen theory as well as the reliability of the simulation tool. This book is addressed to researchers who are interested in physics of surfaces and interfaces, but also to engineers who would like to improve the interfacial properties of fibers, yarns, and textiles.