Polymer networks form complex materials and play a vital role as one of the cytoskeleton's main constituents. Since the cytoskeleton acts as the structural element of the eucaryotic cell, its investigation is crucial for the understanding of a variety of dynamical and mechanical properties in cell biology. In particular, this book focuses on the theoretical description and computer simulation of entangled networks, where the only interaction between polymers is their mutual uncrossability. The presented results fundamentally deepen the understanding of entangled networks of semiflexible polymers. Existing concepts are expanded by quantitative predictions as for example the absolute value of the tube diameter, its length corrections or the absolute value of the modulus. Additionally, new concepts like transient distribution functions and non-affine deformations are introduced and their significance is emphasized.