Over the last twenty-five years, visualization software has evolved into robust frameworks that can be used for research projects, rapid prototype development, or as the basis of richly featured, end-user tools. For this panel, we will describe upcoming challenges facing visualization software in five categories: programming models for future architectures, maximizing performance for future architectures, application architecture and data management, data models, and rendering. Further, for each of these categories, we describe where evolutionary advances are sufficient to meet the visualization software challenges, and posit areas in which revolutionary advances are required.