This article introduces the rationale for developing a special issue on methodological and statistical advancements in clinical assessment, which will appear approximately 25 years after a similar 1995 issue that produced many seminal and highly cited articles. We commissioned articles from a range of expert scholars in important areas of psychometrics (reliability, validity, scale construction, item response theory, and factor analysis) and assessment methodology in specific contexts (multicultural, clinical prediction, response bias, experience-sampling, and neuroscience) in addition to a lead article that considers clinical assessment research in the broader open science framework. We briefly summarize these contributions and their impact.