We propose a series of two team meeting at ISSI, aimed at putting together knowledge over a wide range of aspects of the connection between accretion of matter and ejection of relativistic jets in astronomical systems containing a black hole, both inside our galaxy and at the center of other galaxies, joining observational to theoretical approaches. The meeting of a selected number of geographically-scattered scientists, focussed on these topics, will allow to achieve results which are not within reach in the framework of smaller local collaborations. The physics of the ejection of relativistic jets is largely unknown. The main question to be answered is: how is the matter prevented from falling into the black hole, to be collimated and ejected from the system at relativistic velocity? The most promising way to obtain an answer is to study the relation between the jets and the observed properties of the accreting flow. The main goals of the meeting are to establish scaling laws to connect systems of widely different masses and to obtain a robust estimate of the role of jet ejection in the observed high-energy properties. These are key properties to reach a global understanding of the accretion/outflow relation. The knowledge of the relative energetics of the accreted and ejected flow, together with the identification of basic parameters that scale over many orders of magnitude, will open new views to our understanding of the mechanism of jet production. As not only the expertise, but also the data are scattered through among different groups, it is crucial to bring the relevant researchers together within a common project.