There is a distinct lack of research into the concept of acute mental health crisis. Without investigating the concept of crisis itself, it is not possible to appreciate the attributes of crisis so that it can be measured. This has hampered the development of good psychometric tools for crisis. The aim of this research was to develop the first standardised, valid and reliable measure for the assessment of people presenting to Crisis Resolution and Home Treatment (CRHT) teams. This research utilised qualitative and quantitative research techniques to develop a crisis measure starting with a comprehensive investigation into the concept of acute mental health crisis to identify an item pool and clinically credible item rating scale. A prototype crisis measure was developed and piloted in two NHS CRHTs and data collected. This data was analysed to identify the key areas of crisis assessment (the subscales), a flexible rating scale and scoring system creating a measure named the Crisis Risk and Adaptive Functioning Tool (CRAFT). The CRAFT provides patient crisis profiles highlighting areas of strength, resilience, weakness and vulnerability. A thorough investigation of crisis was completed with CRHT staff and patients through interviews and focus groups. An initial 143 item pool and clinically credible item rating scale were identified and developed into a prototype pilot crisis measure. This measure utilised a flexible rating approach encapsulating both risk and protective factors believed to reflect clinical practice. The measure was piloted and the data analysed to assess the structure of the crisis measure’s item pool using the statistical techniques of Principal Component Analysis (PCA) and Rasch analysis. These analyses resulted in a 66 item measure with 8 unidimensional subscales including; 1) Crisis Recovery Indicators, 2) Adaptive Decision Making, 3) Risk of Harm to Self, 4) Mediating Factors, 5) Daily Structure, 6) Risk of Harm to Others, 7) Feelings and Affect, and 8) Basic Needs. The total variance explained by these 8 subscales was 67.6% with excellent internal reliability as indicated by a Cronbach’s alpha coefficient of 0.98 (p<0.001) and temporal reliability indicated by Spearman’s correlation of 0.971 (p<0.001, one tailed). This suggests that this measure has a strong internal structure and provides stable outcomes over time at both the subscale and global overall measurement levels. Receiver Operator Characteristic curve analysis supported the identification of cut-offs to indicate low, moderate and high levels of crisis and were shown to have good levels of sensitivity and specificity for the crude discrimination between individuals who require CRHT treatment and individuals who do not require CRHT treatment (sensitivity 0.89 and specificity 0.73) and for accurately discriminating between the basic treatment levels of low, moderate and high (sensitivity 0.80; specificity 0.69). One of the great advantages of utilising the Rasch model is that it supports the identification of key characteristics from an item pool. Application of the subscales and the overall measure to the Rasch model identified items that were most representative of underlying constructs and risk, highlighting items of essential essence for assessing crisis in the context of community treatment. These items may act as useful clinical and risk indicators for community assessment. After considering the evidence from the PCA and Rasch analysis for the underpinning construct, the measure was named the Crisis Risk and Adaptive Functioning Tool (CRAFT) to encapsulate both the risk and adaptive functioning (coping and management) aspects measured by the tool. There are a number of clinical implications resulting from the development of CRAFT for the assessment of crisis. This research clearly identifies 8 key areas for crisis assessment and the specific items that describe them. This promises to be a powerful clinical tool as it clarifies the main areas of concern and importance for crisis assessment and provides mental health professionals with a means of assessing and monitoring patients experiencing crisis. In addition to the clinical benefits offered by the CRAFT, it provides an approach to assessing and monitoring crisis to support further research in the area of acute mental health crisis. This research offers significant steps towards the development of a quality measure for crisis assessment. However, it is acknowledged that the process of measurement development is never complete. It simply evolves over time with the aim of coming closer to the valued direction.