Relational continuity of care (RCC), the ongoing interpersonal and therapeutic relationship built up between a patient and a specific primary care clinician over time, is central to effective primary care delivery. Sixty years of evidence link higher RCC to improved patient experience, fewer hospital admissions, and lower mortality, as well as other important benefits for healthcare systems, such as lower cost.1-3 Despite these benefits, RCC is declining across healthcare systems internationally. Research has demonstrated this in the UK and US,4 but as neither country runs systematic nationwide continuity measurement this needs validating in practice. Continuity measurement is the first step to improvement, and here lies an opportunity for cross-national learning about how to increase continuity. There is also an opportunity to combine efforts to identify the infrastructures, policies, and practices needed to make these efforts a success and to improve the RCC that is delivered. The contrasting healthcare systems in the UK and US have their own opportunities and challenges for measuring and improving RCC. In the UK, universal patient registration to a general practice and a single point of access to health care provide an opportunity to deliver relational care, though this may be limited by the increasing number of patients that each practice is now accountable for. The practice-based model offers the potential for local innovation, and for continuity measurement and improvement to become part of routine operational practice, although scaling success or measuring impact nationally can be difficult. In contrast, the US benefits from rich national datasets that enable large-scale continuity-outcomes analyses, but measures are typically retrospective and remain poorly integrated into practices' day-to-day decision making. In addition, the absence of universal registration and multiple routes of access to primary care can make patient attribution a challenge, though the payment structures within the ...