BackgroundRecent studies have suggested engagement is linked with beneficial outcomes for individuals and organisations. Despite growing demand for resources and advice on engagement within the NHS, there has been no systematic evaluation of how engagement strategies can be developed and operationalised within the NHS.Objectives and research questionsTo evaluate evidence and theories of employee engagement within the NHS and the general workforce to inform policy and practice. Four research questions focused on definitions and models of engagement; the evidence of links between engagement and staff morale and performance; approaches and interventions that have the greatest potential to create and embed high levels of engagement within the NHS; and the most useful tools and resources for NHS managers in order to improve engagement.Review methodsEvidence was evaluated using a narrative synthesis approach involving a structured search of relevant academic databases and grey literature. The search yielded a final data set of 217 items, comprising 172 empirical papers, 38 theoretical articles, four meta-analyses and three books. From the grey literature, only 14 items were used in the analysis.Main findingsThere is no one agreed definition or measure of engagement. Existing approaches were grouped under three headings: a psychological state; a composite attitudinal and behavioural construct; and employment relations practice. Most fell under the first category, with the Utrecht Work Engagement Scale being the most prevalent. Most theorising around engagement used the job demands–resources framework. Thirty-five studies considered engagement and morale, and the most consistent finding was a positive link between engagement and life satisfaction, and a negative link between engagement and burnout. Some studies suggested that engagement was positively associated with organisational commitment and job satisfaction and negatively linked to turnover intentions. Of 42 studies that looked at performance and engagement, the strongest support was found for a link between engagement and individual in-role performance and a negative link between engagement and counterproductive performance outcomes. A link between engagement and higher-level performance outcomes was also found. Of 155 studies that explored approaches and interventions that promote engagement, the strongest support was found for the following: positive psychological states including resilience; job-related resources and job design features; positive leadership; perceived organisational support; team-level engagement; training and development. Only a small proportion of studies were based in health-care settings, making the application of evidence to wider contexts limited. Studies identified in the grey literature suggested that the focus of practitioner material was more on wider managerial issues than on psychological factors.ConclusionsThe synthesis highlights the complex nature of the engagement evidence base. The quality of evidence was mixed. Most studies were cross-sectional, self-report surveys, although the minority of studies that used more complex methods such as longitudinal study designs or multiple respondents were able to lend more weight to inferences of causality. The evidence from the health-care sector was relatively sparse. Only a few studies used complex methods and just two had taken place in the UK. The evidence synthesis suggests that employers might consider several factors in efforts to raise levels of engagement including development and coaching to raise levels of employee resilience, the provision of adequate job resources, and fostering positive and supportive leadership styles.FundingThis project was funded by the National Institute for Health Research (NIHR) Health Services and Delivery Research (HSDR) programme.