Open Access Highly Accessed Research article

Understanding the implementation of complex interventions in health care: the normalization process model

Carl May1*, Tracy Finch1, Frances Mair2, Luciana Ballini3, Christopher Dowrick4, Martin Eccles1, Linda Gask5, Anne MacFarlane6, Elizabeth Murray7, Tim Rapley1, Anne Rogers5, Shaun Treweek89, Paul Wallace10, George Anderson2, Jo Burns7 and Ben Heaven1

Author Affiliations

1 Institute of Health and Society, Newcastle University, 21 Claremont Place, Newcastle upon Tyne, NE2 4AA, UK

2 General Practice and Primary Care, University of Glasgow, Glasgow, UK

3 Agenzia Sanitaria Regionale – Regione Emilia Romagna, Bologna, Italy

4 School of Population, Community and Behavioural Sciences, University of Liverpool, Liverpool UK

5 National Primary Care Research and Development Centre, University of Manchester, Manchester, UK

6 Department of General Practice, Clinical Science Institute, National University of Ireland, Galway, Ireland

7 Department of Primary Care and Population Sciences, Royal Free and University College Medical School, London, UK

8 Community Health Sciences Division, University of Dundee, Dundee, UK

9 Nasjonalt Kunnskapssenter for Helsetjenesten, Oslo, Norway

10 UK Clinical Research Network, London, UK

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BMC Health Services Research 2007, 7:148  doi:10.1186/1472-6963-7-148

Published: 19 September 2007



The Normalization Process Model is a theoretical model that assists in explaining the processes by which complex interventions become routinely embedded in health care practice. It offers a framework for process evaluation and also for comparative studies of complex interventions. It focuses on the factors that promote or inhibit the routine embedding of complex interventions in health care practice.


A formal theory structure is used to define the model, and its internal causal relations and mechanisms. The model is broken down to show that it is consistent and adequate in generating accurate description, systematic explanation, and the production of rational knowledge claims about the workability and integration of complex interventions.


The model explains the normalization of complex interventions by reference to four factors demonstrated to promote or inhibit the operationalization and embedding of complex interventions (interactional workability, relational integration, skill-set workability, and contextual integration).


The model is consistent and adequate. Repeated calls for theoretically sound process evaluations in randomized controlled trials of complex interventions, and policy-makers who call for a proper understanding of implementation processes, emphasize the value of conceptual tools like the Normalization Process Model.