Phosphorus is only the eleventh most abundant element in Earth’s crust, yet it plays a vital role in biological processes and global food production. In polymer science, phosphorus compounds are widely used as flame retardants, stabilizers, and functional monomers. Over the past two decades at Empa, our research has focused not only on the design of novel phosphorus compounds and their synthetic pathways, but also on understanding their performance under application-relevant conditions. In this presentation, we will highlight the development and application of phosphorus-based flame retardants for both thermoplastic and thermoset materials, drawing on perspectives from academia and industry. In addition, we will present our strategy for creating recyclable, fire-resistant thermosets by incorporating specially designed phosphorus moieties.