Aspects of holography and higher spins in three-dimensional asymptotically flat spacetimes

This thesis deals with the application of the holographic principle to asymptotically flat spacetimes in three dimensions, with a particular focus on higher-spin generalisations of Einstein gravity. The inquiry about different examples of holographic theories apart from well-studied AdS/CFT implementations, in particular such models that include (quantum) gravitational theories relevant to observable physics, is an imperative step towards a broadened understanding of the overall applicability of the holographic principle. Simultaneously, the existence of non-trivially interacting higher-spin theories in flat spacetimes poses an interesting question on itself.