  The technique of muon spin rotation ({\mu}SR) has emerged in the last few
decades as one of the most powerful methods of obtaining local magnetic
information. To make the technique fully quantitative, it is necessary to have
an accurate estimate of where inside the crystal structure the muon implants.
This can be provided by density functional theory calculations using an
approach that is termed DFT+{\mu}, density functional theory with the implanted
muon included. This article reviews this approach, describes some recent
successes in particular {\mu}SR experiments, and suggests some avenues for
future exploration.
