The greatest risk to persons engaging in international medical emergency response is poor preparation. The In Control handbook hopes to provide a remedy. At the time of writing, we are living through the Coronavirus (COVID-19) pandemic, a health emergency that disregards physical borders, brings into focus social inequalities and affects people on every continent. This shared challenge requires unprecedented measures and the collaboration of the brightest minds to support global health protection through this crisis and beyond. Healthcare infrastructures have to be strengthened, public health capacities and processes upgraded, medical countermeasures and vaccinations found and psychosocial side-effects treated. Solidarity is the normative order of the day and the human species has to collaborate to face this invisible threat. Hiding and living in fear is not an option in this interconnected world. We have both a responsibility and an opportunity to make substantial contributions to a safer, healthier and more sustainable future for us all. The existence of this handbook is an impressive example of solidarity. Over 50 authors from more than 15 institutes and organisations have come together voluntarily within a very short time to make their expertise available and enable cross-sectoral thinking. Knowledge is bundled, resources are combined, information gaps are filled. The In Control handbook is not a theoretical treatise of possible dangers, but a collection of subject-matter expertise, written by experts and practitioners who have shaped health topics over the past 20 years in the most diverse corners of the world. The Centre for International Health Protection at the Robert Koch Institute (RKI) is collaborating with its partners and investing heavily in the build-up of operational know-how and capacity to support health crisis response abroad. This is done by preparing and enabling professionals to deploy safely across the world to assist those in need. In Control addresses the multi-faceted challenges of an international deployment. Readers will find not only technical medical information, but also insights into, for example, the fragility of our environment, the cultural differences that influence risk communication or the dilemmas arising from social distancing. Legal principles are highlighted, along with ethical guidance to ensure that our actions and decisions correspond to the highest moral standards.