This paper discusses six challenges relevant to Web-based testing. Some of these challenges are not specific to Web-based testing, but generalize to all computer-based testing. The challenges are: (1) security and using test centers for Web-based testing; (2) measuring complex skills and problem-solving tasks on the Web; (3) integrating modern item selection and test assembly algorithms; (4) storing and processing all relevant examinee response data; (5) the large-scale distribution of "high-bandwidth" tests (e.g., multimedia, high-density audio video, or images); and (6) optimal ergonomic design of Web-based testing interfaces. Considering each of these challenges raises questions about the future of Web-based testing and supports the need for better education across many sectors of the Web-based testing community about the technical aspects of psychometrics and high-stakes testing needs. In addition, there must be adherence to standards and principles of professional practice and science. (SLD)