David A. Richards is Professor of Mental Health Services Research at the University of Exeter Medical School. For many years he has been at the forefront of national and international efforts to improve access to treatment for those suffering from high prevalence mental health problems such as depression. A nurse by professional background, he is a UK National Institute of Health Research Senior Investigator, President of the European Academy of Nursing Science and chair of the European Science Foundation REFLECTION Research Network Programme, an interdisciplinary European Faculty of researchers, equipped to design, plan and implement programmatic, mixed methods and complex interventions research. Like Ingalill, he has frequently challenged the research community to reduce waste in their work by refocussing their research activity towards clinically relevant programmes, driven by the uncertainties of clinical practice and the real concerns of the public, patients and clinicians.

Ingalill Rahm Hallberg is Professor in Health Care Science at Lund University, Sweden. She has been the pro-dean of the Medical Faculty, the assistant vice-chancellor and pro vice-chancellor of Lund University. She is a nurse by professional background. Her research has been on aging, care and services for older people and living with severe diseases, an area in which she has been at the forefront nationally and internationally. Her frequent involvement in reviewing research proposals, research at universities and by research groups nationally and internationally inspired her to initiate a debate on how research was very often scattered, lacking coherent programmes and dominated by descriptive studies with no impact on health care. As the previous president of the European Academy of Nursing Science she was, together with David, a driving force to change the unwelcome preponderance of small-scale, descriptive projects.

Foreword 1. The Complex Interventions Framework 2. Knowledge for Healthcare Practice 3. The Value of Mixed Methods for Researching Complex Interventions 4. The Critical Importance of Patient and Public Involvement for Research into Complex Interventions Part 1: Developing Complex Interventions Part 1 Introduction 5. Systematic Reviews of the Effects of Interventions 6. Advanced Approaches to Evidence Synthesis and its Application to Intervention Design 7. Exploring Complexity in Systematic Reviews of Complex Interventions 8. The Synthesis of Qualitative Data 9. Building a Case for Mixed Method Reviews 10. Development of Complex Interventions: Outcome Modelling 11. Designing Interventions to Change Health-related Behaviour 12. Modelling Process and Outcomes in Complex Interventions Part 2: Investigating the Feasibility and Undertaking Pilot Testing of Complex Interventions: An Introduction Part 2 Introduction 13. Pilot Studies and Feasibility Studies for Complex Interventions: An Introduction 14. How to Use Feasibility and Pilot Trials to Test Alternative Methodologies and Methodological Procedures Prior to Full Scale Trials 15. How to Use Feasibility Studies to Derive Parameter Estimates in Order to Power a Full Trial16. Addressing Issues in Recruitment and Retention Using Feasibility and Pilot Trials 17. Testing the Waters: Piloting a Complex Intervention 18. Feasibility in Practice: Undertaking a Feasibility Study to Answer Procedural, Methodological and Clinical Questions Prior to a Full-scale Evaluation Part 3: Evaluation of Complex Interventions Part 3 Introduction 19. Individually and Cluster Randomised Trials 20. Stepped Wedge, Natural Experiments and Interrupted Time Series Analysis Design 21. Non-standard and Preference Designs 22. Single-subject Designs 23. Process Evaluation of Complex Interventions: A Summary of Medical Research Council Guidance 24. Intervention Fidelity in Clinical Trials 25. Qualitative Process Evaluation for Complex Interventions 26. Economic Evaluations of Complex Interventions Part 4: Implementation of Complex Interventions Part 4 Introduction 27. Implementation Issues: Towards a Systematic and Stepwise Approach 28. Why do Barriers and Facilitators Matter? 29. How to Arrive at an Implementation Plan 30. Applying Normalization Process Theory to the Implementation of Complex Interventions 31. Action Research for the Implementation of Complex Interventions 32. Systems Modelling for Improving Healthcare 33. A Few Final Thoughts