EEG is a valuable tool in clinical research with the potential for broader use in clinical practice. It is commonly used in the early phases of clinical research as an objective tool for studying disease pathophysiology, pharmacodynamic effects on brain activity, and biomarker development. Despite its promise, adoption in routine clinical care remains limited due to the lack of standardized parameters—such as channel number, processing pipelines, analysis techniques, and recording duration—as well as concerns about inter-rater reliability. These challenges have slowed translation, yet EEG continues to play a growing role in exploring biomarkers, disease onset and progression, and therapeutic outcomes. This chapter first defines clinical research and covers why EEG is a cost-effective, beneficial tool for clinical applications. It highlights applications where the use of EEG is well established, such as in epilepsy and sleep research. The chapter also covers more novel applications of EEG as a biomarker in neurodegenerative disease and assessment of drug efficacy in clinical trials. The chapter then ends on the future of using electrophysiology more widely in clinical settings, including using spectral fingerprints and EEG connectivity patterns for evaluating disease onset and progression.