The PhenX Toolkit provides the research community with a core set of high-quality, well-established, low-burden measures intended for use in genome-wide association studies and other population-based studies. More specifically, the PhenX Toolkit will make it easy for researchers to effectively expand a study to include standard measures outside of their primary research focus. Broad acceptance and use of PhenX measures will promote cross-study comparisons to increase statistical power for identifying and replicating variants associated with complex diseases and with gene-gene and gene-environment interactions. The hope is that the PhenX Toolkit will be widely adopted by the scientific community, fostering a new era of cooperation and collaboration and facilitating cross-study, transdisciplinary, and translational research.