Volume visualization refers to the visualization of functional phenomena in 3D space. At positions in 3D, we are given scalar values, vectors, or tensors (higher dimensional data). The primary focus of this chapter is on two techniques, contouring and direct volume rendering, for visualizing a scalar-valued function defined over a volume. Some attention is given to visualizing vector fields and tensors (higher dimensional phenomena). Finally, we bring attention to the relatively new field of haptic visualization.