This chapter summarizes several constitutive models that are appropriate for capturing the mechanical response of soft biological tissues. Some of the theory is based on the general elastic framework for fiber-reinforced materials discussed in Chap. “ Constitutive Theory of Nonlinear Elasticity ” [43]. A primary focus is on the analysis of the effect of the dispersion of collagen fibers via the generalized structure tensor and the angular integration (AI) approaches and the discrete version of the AI model. The effect of fiber recruitment is also discussed. A significant part of the chapter is devoted to the modeling of inelastic behavior, including damage and anisotropic finite strain viscoelasticity using a fractional derivative approach followed by a general framework for the analysis of poroviscoelasticity of soft biological tissues. Particular attention is given to the properties of the volumetric part of the equilibrium energy function. In the final section a representative example based on the elasticity and viscoelasticity of the myocardium is provided.