We describe a classification scheme that we believe provides a more structured framework for reasoning about parallel rendering. The scheme is based on where the sort from object coordinates to screen coordinates occurs, which we believe is fundamental whenever both geometry processing and rasterization are performed in parallel. This classification scheme supports the analysis of computational and communication costs, and encompasses the bulk of current and proposed highly parallel renderers - both hardware and software. We begin by reviewing the standard feed-forward rendering pipeline, showing how different ways of parallelizing it lead to three classes of rendering algorithms. Next, we consider each of these classes in detail, analyzing their aggregate processing and communication costs, possible variations, and constraints they may impose on rendering applications. Finally, we use these analyses to compare the classes and identify when each is likely to be preferable.< >