This Funding Opportunity Announcement (FOA) invites applications that seek to improve the availability, quality, and utility of data and measures that capture multimorbidity or multiple chronic conditions (MCCs) and the methods for analyzing multimorbidity data. Research supported by this initiative should be designed to discover, develop, and/or evaluate MCC measures/tools that reflect the longitudinality and life course diversity of multimorbidity. This includes but is not limited to measures/tools to support basic mechanistic discovery of shared MCC pathways using animal models of MCCs, and identification and initial biological, analytical, and clinical evaluation of MCC shared signatures. Also sought are patient-focused studies that capture patient reports and related constructs such as functional limitations and quality of life; analytic approaches best suited for use with multimorbidity data and matched to target populations; and approaches that fully harness the wealth of multimorbidity data available in EHR systems. Studies may make use of existing data and data linkages to explore new research questions related to co-occurring MCCs. Prospective applicants whose research interests relate to studies that identify shared mechanisms or development of innovative interventions to address MCCs should see PAR-XX-XXX.