Background: Improving access to psychological therapies for people with common mental health problems will make a significant impact on distress and disability. Currently, patients with mental health problems such as anxiety and depression experience limited treatment choices. Psychological therapies services are often characterised by relative inaccessibility and long patient waiting times. Stepped care systems incorporating self-help and low intensity psychological interventions have been recommended in NICE guidelines and may improve this situation. However, stepped care systems are complex and require considerable reconfiguration of existing services. The acceptability and flow of patients through such systems cannot be predicted with authority from current knowledge. Aims: To design effective and efficient stepped care systems for psychological therapies in a variety of settings through stakeholder consensus exercises, facilitated by computer modelling to forecast patient To investigate the effect of implementing these systems on patient access, throughputs, clinical outcomes and patient choice; To identify barriers to the implementation of stepped care; To investigate the generalisability of the reconfiguration process including the utility of an implementation manual and computer modelling tool Research type and location: An operation research study using stakeholder consensus exercises facilitated by computer modelling, data from systematic reviews and case study data collection in four Phase I and ten Phase II mental health settings providing mental health care for people with common mental health problems. Methods of working: Stakeholders will develop service redesigns via a consensus building procedure, informed by Patient Progress Models, to assess the likely performance of service reconfiguration options in terms of patient throughput and capacity needs for different system 'steps'. Initially, models will be based on published epidemiological and outcome data, albeit incomplete, However, as the study progresses, data from study sites concerning: patient preferences, needs, flows, access, outcomes and waiting times will be used to adjust services to maximise their effectiveness and efficiency. Measures of outcome: - Service structure: capacities of steps; referral routes; qualifications and professional orientation of clinicians - Service processes: patient waiting times; numbers of patients entering the service; modality of treatments offered, chosen and received by patients; number and duration of therapy sessions attended - Patient characteristics: diagnostic and demographic data on patients seen by the service - Patient clinical outcomes (CORE-OM), health related quality of life (SF36), health state utilities (EQ5D), patient experience and acceptability of stepped care - Clinical staff and service managers' views on the process of both service reconfiguration and delivery of stepped care