The rapidly increasing deployment of AI raises societal issues about its safety, reliability, robustness, fairness and moral integrity. This paper reports on a declaration intended as a code of conduct for AI researchers and application developers. It came out of a workshop held in Barcelona in 2017 and was discussed further in various follow up meetings, workshops, and AI schools. The present publication is a matter of historical record and a way to publicize the declaration so that more AI researchers and developers can get to know it and that policy makers and industry leaders can use it as input for governance. It also discusses the rationale behind the declaration in order to stimulate further debates.