“Evidence-based medicine” has been hailed as the “new paradigm” for health care. This paper defines evidence-based practice, describes its development and growing importance, explains why randomized controlled trials are the “gold standard” for evidence about the effectiveness of specific therapeutic methods, warns about reaching conclusions based on any single study, and points the reader towards good sources of information on how to assess the relevance of findings from published studies and systematic reviews of the most reliable evidence regarding particular components of the care of pregnant women. As a result of those reviews, specific elements of perinatal care have been classified into categories based on their usefulness or harmfulness when applied to low-risk women. The paper goes on to summarize the evidence regarding three intrapartum practices that are demonstrably safe and useful and “should be encouraged” and four intrapartum practices that have trade-offs between beneficial and adverse effects and are “frequently used inappropriately.” Some of the most beneficial elements of intrapartum care are not available to most women who give birth in American hospitals, and some practices that are useful but have adverse effects are being provided to an ever-expanding proportion of women J Nurse Midwifery 1999;44:355–69 © 1999 by the American College of Nurse-Midwives.