Outcome measurement is important to clinical practice--yet outcome many speech and language therapists find it difficult to apply measures in practice, and not all clinicians and services have been able to implement and/ or use outcome measurement successfully. To date there has been little research to explain why implementation is often unsuccessful, and to provide clinicians and managers with direction as to the likely barriers and facilitators which should be considered. To develop a theoretical framework to explain the implementation and use of outcome measurement in clinical practice by speech and language therapists. A qualitative, inductive theory-building approach, using grounded theory methodology, was applied. This included theoretical sampling, constant comparison, memo writing, and theoretical integration. Participants were 16 Australian managers and clinicians who were using, or who had used, outcome measures. The resulting theoretical framework explains two interactive stages that occur when speech pathologists attempt to use outcome measurements in practice. First, clinicians must 'try on' outcome measurement in their own context, examining the way it fits with existing areas, such as their normal practices and priorities, and the wider group and organizational context. Having identified where outcome measurement does not 'fit', clinicians attempt to 'align' outcome measurement with the context (or vice versa), in order to create a better fit between the two. Strategies of 'tailoring' outcome measurement (e.g. using only parts of a measure) or 'accommodating' outcome measurement (e.g. changing routines to allow time for outcome measurement ratings) are possible, but are dependent on clinicians having a true picture of outcome measurement, the role and need for the data, and the existing context. Clinicians must also have control over the areas that need to change in order for outcome measurement and the context to 'align'. Where outcome measurement and the context can be aligned, outcome measures are more easily used. The theory provides a framework for considering the use of outcome measurement in clinical practice. Implications for implementing outcome measurement in clinical practice are discussed, including the need to clarify the role and need for the data; the requirement that clinicians understand how outcome measurement fits with context outside of their own personal purview; and the need for managers to support change to areas that are outside of the control of clinicians.