Volume rendering is a compute and memory intensive application. Researchers have attempted to use parallel computers to speed up volume rendering for interactive frame rates. Many architectures and approaches have been developed. I developed a taxonomy of volume rendering by forming five categories: algorithm control flow, targeted hardware, application data characteristics, visualization method, and publication specifics. I discuss the current approaches in parallel volume rendering algorithms, and show how different taxonomies from the developed classification provide the ability to compare, contrast, and show potential for future research results. 10 Pages