Iron-based superconductors contain layers of iron and a pnictogen – such as arsenic or phosphorus – or a chalcogen, like oxygen or selenium. Previously dismissed eas weak candidates for superconductivity, iron-based superconductors took the science community by surprise when it was discovered that the new iron arsenide family had very high transition temperatures. Since then these high-temperature superconductors have become a hot topic of research, with neutrons and muons playing an essential role in investigating their unusual properties, in order to help quantum physics develop a theory behind high-temperature superconductive materials.