This article outlines the capabilities of a scientific visualization toolkit called Data Viewer and compares it to analogous software. DataViewer was originally designed for the construction of the visualization part of certain computational steering packages, and consequently it is particularly straightforward to closely couple DataViewer with numerical calculations. Rendering is performed through a highlevel scene graph which facilitates the easy construction of complex visualizations. Data Viewer differs from other such libraries by allowing complex geometrical objects, which efficiently encapsulate large amounts of data, to be used as. nodes in the scene graph. Graphics hardware access is through the OpenGL API.