Injections are routinely administered by nurses in acute care settings and in the community. Nurses require a thorough understanding of anatomy and physiology, pharmacological principles and equipment, and potential risks to the patient of injections. Nurses should also take an active approach to patient assessment before injecting medicines. This article, the first of two, provides an evidence-based review of injection administration, with particular reference to subcutaneous injections, and suggests a framework for best practice.