Excellent usability characteristics allow electronic health record (EHR) systems to more effectively support clinicians providing care and contribute to better quality and safety. The Office of the National Coordinator for Health IT (ONC) therefore requires all vendors to follow a User-Centered Design (UCD) process to increase the usability of their products in order to meet certification criteria for the Safety-Enhanced Design part of the Meaningful Use (stage 2) EHR incentive program. This report describes the initial stage of a UCD process in which foundational design concepts were formulated. We designed a functional prototype of an EHR module intended to help clinicians to efficiently complete a summary review of an electronic patient record before an ambulatory visit. Cognitively-based studies were performed and the results used to develop a cognitive framework that subsequently guided design of a prototype. Results showed that clinicians categorized and reasoned with patient data in distinct patterns; they preferred to review relevant history in the assessment and plan section of the most recent note, to search for changes in health and for new episodes of care since the last visit and to look up current-day data such as vital signs. These basic concepts were represented in the design, for instance, by screen division into vertical thirds that had historical content to the left and most recent data to the right. Other characteristics such as visual association of contextual information or direct, one-click access to the assessment and plan section of visit notes were directly informed by our findings and refined in a series of UCD-specific iterative testing. Understanding of tasks and cognitive demands early in the UCD process was critically important for developing a tool optimized for reasoning and workflow preferences of clinicians.