Non-collinear magnetism arises when the spins in a material are not all aligned along a single axis leading to rich phenomena such as spin spirals, skyrmions, and frustrated magnetic states. Density functional theory (DFT) provides a framework to study these systems from first principles, allowing the investigation of spin textures, energetics, and local magnetic fields. In this talk I will introduce the concepts and practical implementation of non-collinear magnetism in DFT, highlight computational challenges, and illustrate the approach with examples from real materials and calculations, including cases where theory directly informs and interprets experimental results such as muon spin spectroscopy.