The use of computers has become well established throughout the business enterprise; but computer usage within the health care sector has lagged, particularly for automation of interactions between individual clinicians and their patients. A number of factors have contributed to this including difficulties in representing medical knowledge in computer-processible formats, the limited application of standards for data recording and transmission, and problems in human-computer interaction.A major obstacle to the use of computers in medicine has been the stationary nature of desktop computers. Most clinicians are mobile knowledge workers who need access to information across a wide variety of settings: in offices, exam rooms, emergency departments, hospitals, nursing homes and at home. Within each setting, there is concern that a large box on the consultation desk may interfere with communication between clinicians and patients. Moreover, many physicians do not have keyboard skills. Even for those who can type, keyboard data entry---concomitant with interviewing and examination-- is difficult. To overcome these obstacles, our group at the Yale Center for Medical Informatics has developed systems that operate on small, mobile platforms and accept pen-based data entry.We recognized early on that systems would have to be integrated tightly with clinical workflow and provide benefits to offset the inconvenience associated with their use. Clinical workflow refers to the complex interacting tasks performed by clinicians as they go about their daily work and to the corresponding information flows that are generated. A particular interest has been in providing clinical decision support at the point-of-care. We have extracted knowledge from evidence-based clinical practice guidelines and embedded it in mobile, pen-based systems that inform decision making by clinicians.