Systematic reviews are important as a key source of information for commissioners and for developing practice in speech and language therapy (SLT) and early years. Interventions in this field are often complex and are delivered in community settings. This paper applies a systematic review of environmental interventions in early years for children with speech, language and communication needs. Interventions for primary language impairment may be divided into those which are child-focused and those which are focused on the environment. In both cases, the aim is to effect changes in the child's language skills. The paper introduces the context of evidence-based practice and commissioning of such interventions and argues that systematic reviews may be combined with other evidence to provide information which is fit for purpose for commissioners and for practitioners in the field.