Tiller is a tool for the interactive analysis of four-dimensional data. It is based on a powerful yet simple interface consisting of two windows. One displays an image representing two data dimensions, the second presents a grid where the user can interactively select points. Selecting single points prompts Tiller to display individual images, allowing basic data browsing. Sequences of points may also be specified to rapidly produce custom animations. The ability to produce such animations quickly is an effective way to explore data where the interesting aspects and structure may not be known in advance. To date we have used Tiller primarily for the visualization of time series volumetric data. For each time step, we computer projections of the volume at different angles of rotation. Viewing the sequence of projections for one time step corresponds to visualizing the volume rotating around one axis. After computing the set of renderings for each time step, we use Tiller to view the data and to define animation sequences. The horizontal axis of the Tiller grid represents the rotation angle of the volume during rendering, the vertical axis represents time. Working with the grid, it is simple for the user to find interesting viewing angles and time intervals and to produce movies highlighting important aspects of the data. Currently we compute the volume renderings in advance and store them on disk. Our future plans are to utilize the same Tiller interface as the front-end to a real-time volume rendering application utilizing supercomputers such as the Connection Machine or the Cray.