Childhood obesity is a major public health problem leading to short-term and long-term adverse health outcomes, reduced quality of life and high societal costs. Obesity and related comorbidities seem to originate in the earliest phase of life. Adverse maternal and offspring lifestyle factors in the preconception period, pregnancy and earlychildhood are major risk factors for childhood obesity and its comorbidities. These adverse maternal and offspring lifestyle factors are highly prevalent, cluster within families and are modifiable risk factors for childhood obesity. Urgent development of evidence-based childhood obesity prevention strategies targeting these family-based lifestyle factors in these three crucial transition periods is needed. These prevention strategies need to be developed in strong collaboration with consumers and stakeholders to enable effective large-scale implementation. EndObesity will develop, implement and evaluate innovative, multi-disciplinary strategies for prevention of childhood obesity by targeting family-based lifestyle factors in the preconception period, pregnancy and earlychildhood, covering the first 1000 days of life. EndObesity includes transnational European experts from academia, municipal/governmental health care services, educational stakeholders, industry partners and parentchildhood organizations, and combines outstanding expertise in multiple areas of childhood obesity science and implementation. First, in WP1 and WP 2 we will identify, from preconception to early-childhood, facilitators and barriers for family-based behaviours patterns associated with childhood obesity and develop dynamic populationbased prediction models for early identification of children at high risk of overall obesity and an unhealthy obesity phenotype. Second, in WP3 and WP4 we will develop evidence-based innovative intervention strategies for childhood obesity prevention by optimizing family lifestyle and nutrition in the preconception period, pregnancy and early-childhood using population-level strategies and more personalized intervention strategies for higher risk groups. Finally, in WP5 we will implement and evaluate childhood obesity prevention strategies through novel and existing partnerships with health care, governmental, educational and industry stakeholders and parentchildhood organizations addressing identified facilitators and barriers and using evaluation studies. Ultimately, EndObesity will optimize family-based health behaviours in three crucial transition periods to prevent childhood obesity. This innovative, novel approach is not only beneficial for the child, but for the entire family and will break the transgenerational vicious cycle of obesity.