The macroscopic behavior of fiber-reinforced materials is determined by the properties of embedded fibers, especially their orientation. For example, in biological tissue like skin, aligned collagen fibers are responsible for its anisotropic, non-linear mechanical behavior. In this thesis, novel methods are introduced to investigate the orientation of fiber networks in materials. The adaptive filter method (AF method) was developed to determine the angular orientation distribution without any assumptions on the fiber network. The AF method showed a significantly increased accuracy in determining the dispersion of the fiber network compared to a state-of-the art band-pass method. Its applicability to experimental data was demonstrated by the analysis of in-vivo second harmonic generation (SHG) images of dermal collagen. Collagen fiber networks are reported to consist of multiple fiber families. The Fiber Image Network Evaluation (FINE) algorithm was developed to quantify the number of fiber families and their properties based on the cumulative orientation distribution. Greyscale images with multiple fiber families were simulated using a Monte-Carlo method to benchmark the algorithm. The FINE algorithm was found to reliably determine the number of aligned fiber families and the ratio of anisotropic fibers. Furthermore, morphological changes of the collagen network across skin depth were identified by applying the FINE algorithm to in-vivo SHG images of dermal collagen. Various viscoelastic properties of biological tissue such as creep, strain-rate and strain history-dependence are believed to be related to the collagen fiber network. A multiphoton microscope stretching device was developed to apply mechanical deformations to skin samples, while capturing SHG images of the collagen network at the same time. The FINE algorithm was applied at every state of deformation to track the evolution of the collagen fiber network due to external forces. Cyclic sequences of stretching and relaxation revealed permanent as well as periodical variations of the collagen fiber network of pig skin. A permanent alignment of collagen fibers was associated with the presence of an isotropic fiber family. Furthermore, large differences across the mechanical behavior of samples were successfully related to the initial orientation of their collagen fiber network prior to deformation. The electrical line resistance of novel silver-nanowire photopolymer composites strongly increases with mechanical stretch. To observe changes of the nanowire network during stretching, the FINE algorithm was applied to light microscopy images of these nanowire networks. Nanowires were found to exhibit one isotropic fiber family, that slightly aligns in the stretching direction in case of a low nanowire concentration. However, it was found that the increase in line resistance is dominated by breaking nanowire junctions rather than by their alignment.