Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)I review here form, or textural, birefringence (Delta(F)) in the context of advances in the field, as well as with regard to findings and applications in the physics of photonic devices, fibers maintaining polarization, photonic crystal fibers, and in biopolymers present in extracellular matrices and the myelin sheath. Some advantages of applying knowledge of Delta(F) to biological fields involving biopolymers, especially collagen fibers, are considered in more detail. Tendon and cartilage collagen fibers have been regarded as a model of dense, highly aggregated biopolymers with preferential orientations. Owing to their supramolecular organization, such materials may be used to study molecular order by using anisotropic optical properties, especially Delta(F). Differences between collagen type I-and collagen type II-rich structures, and similarities between collagen crimp and second harmonic generation images are reported. Based on data reported here, it is possible to deduce that collagen type I supramolecular organization has nonlinear optical properties and that tendon segments can conduct red laser light. With respect to nerve fibers, the detection and measurements of Delta(F) have allowed the myelin sheath to be considered a smectic liquid crystal.856365378Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2003/04597-0, 2007/058251-8]