The purpose of the research presented here is to investigate basic physical properties in nonlinear optical materials with delayed or nonlocal nonlinearity. Soliton propagation, spectral broadening and the influence of the nonlocality or delay of the nonlinearity are the main focusses in the work. The research presented in Chapter 3 and papers B and C is concerned with the properties and the stable dark soliton propagation and their bound states in nonlocal nonlinear optical media. It is shown that nonlocality of the nonlinearity induces attractive forces between solitons, that leads to the formation of bound states of out of phase bright solitons and dark solitons. Also, the newly introduced analogy between the nonlocal cubic nonlinear and the quadratic nonlinear media, presented in paper B and Chapter 3 is discussed. In particular it supplies intuitive physical meaning of the formation of solitons in quadratic nonlinear media. In the second part of the report (Chapter 4), the possibility to obtain light with ultrabroad spectrum due to the interplay of many nonlinear effects based on cubic nonlinearity is investigated thoroughly. The contribution of stimulated Raman scattering, a delayed nonlinear optical effect, to this process is shown to be fundamental. Further, the newly developed nonlinear photonic crystal fibers, is shown to be an extremely suitable tool for the process of obtaining light with an ultrabroad spectrum, the supercontinuum generation process. It is the high nonlinearities achievable in these fibers and the possibility to tailor the dispersion properties through precise structure control, that allow various parametric processes to take place. During the project, the process of supercontinuum generation has been studied ”experimentally” via numerical simulations employing a modified nonlinear Schr¨odinger model equation. Chapter 4 and papers D and E are dedicated to this part of the research.