Web users like rich Internet applications (RIAs) because they’re easy to use. But how does the usability of RIA and HTML applications compare? To find out, we evaluated both. We looked for examples of rich Internet and HTML applications in each of four categories and compared how well they supported relevant user goals. We found that, on average, RIAs outperform HTML interfaces; at the same time, RIA usability can fall prey to basic design mistakes. To make the most of their investments, firms planning to invest in RIAs must apply design best practices and run multiple tests on their RIAs before — and after — they go live.