The theological behavior of suspensions of short glass fibers in different fluids has been studied. Transient tests on presheared samples of fiber suspensions in Boger fluids showed that orientation of fibers not only depends on the strain, but also on the rate-of-strain. The experimental results show that upon increasing fiber concentration and/or fiber aspect ratio, the steady shear material functions of fiber suspensions increase at low shear rates, whereas at high shear rates, these material functions approach those of the matrix and become almost independent of fiber characteristics. A theological model based on the modified Jeffery equation for the fiber motion and a Hookean energy model, formulated within the GENERIC framework, for the matrix has been developed to quantitatively predict experimental data for suspensions of fibers in different fluids. A quantitative comparison of experimental data with model predictions shows the ability of the model to predict the theological behavior of fiber suspensions in viscoelastic media.