The Earth Radiation Budget is the global annual mean difference between the incoming solar and reflected solar and emitted terrestrial radiation. It is a small number coming for the difference of two comparably large numbers (TSI and TOR), making its estimation particularly challenging. A positive Earth Energy Imbalance corresponds to the heat continuously accumulated in the Earth's climate system – mainly the oceans, and which will - with a time delay - cause the global warming of the surface and the atmosphere. From the analysis of in-situ observations– mainly based on ARGO, from 2006 to 2020 the mean EEI is 0.76 +/- 0.2 Wm-2, to be compared to a mean EEI of 0.48 0.1 Wm-2 from 1971 to 2020. The exact knowledge of the EEI and its trend is key for a predictive understanding of global warming and assessing the efficiency of global carbon reduction policies. Up to now, heat content measurements of the ocean, land, and atmosphere are used to determine its absolute value. While these in-situ measurements have a great potential, their sampling and trend uncertainty is - despite great improvements over the recent years - not perfect. To determine the EEI with higher accuracy and stability, independent measurement approaches are required. In this session we invite contributions on existing and new measurement concepts with an emphasis on space observations, but also welcome ground-based and in-situ measurements. We also invite modeling efforts that help to better determine the energy storage in the Earth's system and the terrestrial outgoing radiation.