Electronic excitation reaching high energy density is central in many different applications, from materials processing to medical treatments. It emerges when intense radiation arising from sources such as lasers, swift ions, or high-flux X-ray or electron pulses, interact with matter. In general, only partial aspects related to the excitation produced by this type of sources are treated. The lack of a systematic methodology to face the simulation of the underlying phenomena makes it essential to involve scientists from different fields, theoreticians, simulators, and experimentalists. A successful methodology will require smart strategies to make existing solutions, which are appropriate within restricted scopes, work together within a multi scale formalism. The proposed COST Action will tackle this challenge through the following approach 1. Identify and propose experiments to validate simulations as an optimal way to generate progress in the field of intense electronic excitation. 2. Identify the specific role of different radiation sources on electronic excitation-induced effects. This will allow us to connect distinct communities that explore similar effects in parallel. 3. Identify strategies to connect computational methods on different timescales. This will be a central point of the project, since most methods operate reasonably well within their scope of applicability but their coupling to other approaches is not straight forward. 4. Transfer the newly acquired knowledge to industry and societal applications by taking advantage of COST networking tools. This Action aims at creating a network of research groups with expertise in the different parts of the challenge tackled and a common research objective.