Early detection of developmental and behavioral/mental health problems is greatly facilitated when quality instruments are deployed. This article describes how to identify accurate measures and presents standards for screening tests. Included is a table delineating accurate tools for primary care: typically those relying on information from parents (e.g., PEDS, ASQ, PSC, etc.) as well as measures useful in settings where providers have more time and skill at eliciting behaviors from children (e.g., Brigance screens). Screening measures should be used in the context of developmental surveillance; the longitudinal process of incorporating professional observations into decision-making about children's developmental needs. © 2005 Wiley-Liss, Inc. MRDD Research Reviews 2005;11:173–179.