The course deals with constitutive relations of soft biological tissues, i.e. tissues showing large strains. These tissues are non-homogeneous, mostly with fibrous structure. Their structure with various types of fibres and their complex arrangement in the tissue cause their pronounced anisotropic properties with non-linear constitutive relations. A significant hysteresis is also typical for soft tissues; it can be described by linear or non-linear viscoelastic constitutive models, together with creep and stress relaxation. Soft tissues show a lot of other specific properties that cannot be found at technical materials at all (growth, necrosis, change of material properties in response to their load, remodelation, etc.).