Bipolar disorder (BD) is an affective disorder characterized by recurrent major depressive and manic episodes. It is the 7th most burdensome disorder in the global ratings of morbidity, mainly due to its highly recurrent nature, the presence of persistent functional impairment and high risk of suicide. Lithium is the leading treatment for relapse prevention in bipolar disorders. A substantial proportion of patients remain asymptomatic for years on lithium (between 15 to 20%) but others (approximately 30%) do not respond, despite adequate treatment trials of at least 2 years at a therapeutic level. The variability in response to prophylactic lithium is poorly understood and it remains difficult for clinicians to accurately predict which patients will respond without recourse to a lengthy treatment trial. The identification of biomarkers capable of predicting response to lithium is highly desirable, as these would improve long-term management of those with bipolar disorder. Progress in this field would be informed by, and ultimately further inform a more complete understanding of the actions of lithium in the brain. From our current understanding of the actions of lithium, several sources of variability can be proposed to explain the inter-individual Li response variability: absorption; brain/blood pharmacokinetics; transport across the brain barrier; brain lithium concentration and distribution; adherence; biological targets (gene sequence and gene expression); long term physiological effect on brain structures. In this project we propose the creation of a network of scientific cooperation on brain imaging biomarkers of lithium response, and on the molecular signature of lithium response in blood. Collaboration is necessary to achieve the appropriate sample sizes and level of power for these endeavors, especially for predictive brain imaging studies, ‘omics’ studies, the conduct of prospective follow-up studies in which it is desirable to identify patients naïve to lithium. To identify biomarkers of lithium response, there is a strong scientific rationale to present ambitious brain imaging studies, ‘omics’ studies and the combination of the two. The necessary expertise is represented in the proposed network: anatomical MRI (volumes and connectivity), functional imaging, brain lithium content and distribution (MR Spectroscopy), genetic, transcriptomic, proteomic and methylomic. All scientific groups have ongoing research programs on lithium treatment in bipolar disorder. They have all agreed to meet again in October 12, 2015 in Paris to strengthen their ongoing collaborations and set-up new programs. If funded, they have agreed to prepare a project for a H2020 call (SC1-PM-02-2017: New concepts in patient stratification). The participating countries are France, United Kingdom, Italy, Germany, Australia and USA. Nacer Boubenna (European Affairs Officer, H2020 Coordinator of the National Contact Point for the Health challenge) will assist the network for the preparation of the application.So far, no private company is involved in the network but the participation of SMEs will be considered in the future notably for our database management.