Fluctuation-induced interactions are typically forces arising from classical and quantum fluctuations. Paradigmatic examples are the Casimir effect and the van der Waals force. They are connected with a panoply of phenomena of great importance in different areas of physics. The exact knowledge of these interactions is rapidly becoming very important not only for fundamental purposes but also for the opportunities and challenges that they offer to nanotechnology and their impact on future devices.Recent theoretical and experimental investigations have shown that such interactions are tunable in strength and sign, opening new perspectives to investigate aspects of quantum field theory, atomic and condensed-matter physics, and leading to promising and amazing nanoscopic devices.This research targets an intensive theoretical and computational study of equilibrium and non-equilibrium fluctuation- induced interactions. It aims to acquire and enhance the competences in order to affront topics and problematics that are at the root of the future scientific development in all disciplines that deal with nanotechnologies. The methodology adopted will allow to put into evidence special and otherwise hidden features. The increased understanding will also facilitate the genesis of new ideas and the transportability of the results to other frameworks. This project is based on a multidisciplinary approach, combining concepts from different fields of physics, such as equilibrium and non-equilibrium physics, plasmonics, near field radiative heat transfer, diffusive electrodynamics, atomic physics and engineered materials. All these topics are intimately related within the framework of fluctuation-induced interactions, allowing for a complete perspective and physical understanding of these phenomena.