Background: Gestational diabetes mellitus is a potentially serious condition that affects many pregnancies and its prevalence is increasing. Evidence suggests early detection and treatment improves outcomes, but this is hampered by continued disagreement and inconsistency regarding many aspects of its diagnosis. Methods: The Vitamin D and Lifestyle Intervention for Gestational Diabetes Mellitus Prevention (DALI) research programme aims to promote pan-European standards in the detection and diagnosis of gestational diabetes and to develop effective preventive interventions. To provide an overview of the context within which the programme will be conducted and its findings interpreted, systematic searching and narrative synthesis have been used to identify and review the best available European evidence relating to the prevalence of gestational diabetes, current screening practices and barriers to screening. Results: Prevalence is most often reported as 2-6% of pregnancies. Prevalence may be lower towards the Northern Atlantic seaboard of Europe and higher in the Southern Mediterranean seaboard. Screening practice and policy is inconsistent across Europe, hampered by lack of consensus on testing methods, diagnostic glycaemic thresholds and the value of routine screening. Poor clinician awareness of gestational diabetes, its diagnosis and local clinical guidelines further undermine detection of gestational diabetes. Conclusions: Europe-wide agreement on screening approaches and diagnostic standards for gestational diabetes could lead to better detection and treatment, improved outcomes for women and children and a strengthened evidence base. There is an urgent need for well-designed research that can inform decisions on best practice in gestational diabetes mellitus screening and diagnosis. © 2011 The Authors. Diabetic Medicine© 2011 Diabetes UK.