The concept of organisational health originates from fields as diverse as psychology, management, education and occupational health and stems back to the 1950s with the publication 'The Organisation: What makes it healthy'?. One definition states, 'organisational health blends the pursuit of individual wellness with organisational effectiveness (that can be optimised with contemporary business improvement initiatives such as Lean and Six Sigma) to yield a strategy for economic resilience'. In fields outside of healthcare e.g. business and education, correlations have been shown between organisational health and organisational performance (outcome measures), but is the same true in healthcare? At a time of financial difficulty within the NHS, and also with the need for improving patient outcomes, in wake of The Mid Staffordshire NHS Foundation Trust Public Inquiry for example, organisational health could become increasingly important in our hospitals. The methodologies used include systematic review, qualitative interview analysis, questionnaire development, and exploratory and confirmatory factor analyses (EFA & CFA) for questionnaire validation and data collection. This thesis begins with a systematic review of the organisational health literature followed by a qualitative interview study to establish the elements of organisational health for acute NHS Trusts in England. It then describes how, from this data, a pilot questionnaire was developed to measure organisational health and then exploratory factor analysis followed by confirmatory factor analysis techniques were used to create a reliable validated organisational health questionnaire containing 112-items across 8 sections. The next study describes the use of this questionnaire by almost 10,000 NHS staff at 29 acute Trusts in England to measure organisational health. The final study correlates these organisational health scores with hospital outcome measures, revealing that the healthiest organisations have improved outcomes for their patients, including a significantly lower mortality rate.