Portals form the single access point to relevant information and applications for a specific target group. Like all other software systems, portals will get less useful over time if they do not evolve according to changing user requirements. This paper is based on results of approx. 10 projects in Web-Portal research and development between 1997 and 2004. Experience with respect to evolution of the portal platform BaSeWeP is presented from different viewpoints: (1) functional and architectural evolution of the platform from a meta-information system to a knowledge portal, (2) the induced content evolution, and (3) the overall evolution process.