In this issue of Arthritis Care & Research, we present another set of themed articles that are relevant to rheumatology clinical practice and research. Our themed issues are designed to spark interest and influence knowledge growth in rheumatology. The topic for this themed issue is the pertinent use of rheumatology registries, Big Data, and very large patient or administrative data sources to inform patient or individual aspects of key outcomes in the rheumatic diseases. Manuscripts representing a broad range of topics across the lifespan were considered, including treat-totarget, disease burden, costs, as well as other topics, using a wide variety of Big Data sources. Manuscripts submitted for the themed issues of Arthritis Care & Research undergo the same peer-review procedures as other scientific manuscripts in our journal, and therefore meet the same rigorous standards as articles in this or any other issue.The call for articles for this theme issue on Big Data resulted in 76 submissions. From these papers, we are proud to publish 12 articles covering important topics and issues in the rheumatic diseases, including osteoarthritis, rheumatoid arthritis (RA), lupus, juvenile dermatomyositis, and patient care costs. The tremendous response and the wide array of topics addressed by registries, administrative data, and large patient data sources furthered our thoughts on using Big Data in rheumatology and the expected exponential growth in our utilization of these data to increase our understanding of rheumatic diseases. Big Data is an exciting resource that captures nuance and detail, highlighting the evidence in evidence-based medicine for many aspects of disease management that have not been fully appreciated by past study designs or data collection.The volume of Big Data in health care is growing exponentially, outstripping data growth in other sectors and creating both new opportunities and significant challenges for medicine and research. Billions of dollars have been invested in health information technology (IT) infrastructure. Electronic health records (EHRs) have fundamentally changed the work of physicians and health systems. To be a rheumatologist today means spending as many or more hours interfacing with EHRs as with patients. These seismic shifts in medicine have been accompanied by promises of safer, better, and even more cost-efficient care, but to a large extent these promises remain unrealized. Yet, there is reason to be hopeful. Here we discuss the ways the field of rheumatology can harness Big Data to advance our specialty and improve health outcomes for people with rheumatic diseases.What is Big Data? Big Data typically refers to databases or registries with high volume, rapid velocity, much variety, and high veracity. These 4 "Vs" characterize the vast amounts of data that can be aggregated from often disparate sources for analysis. The American College of Rheumatology's RISE (Rheumatology Informatics System for Effectiveness) Registry, a focus for one of the themed articles, is a great exa...