Transition metal-catalysed C–H activation has emerged as an increasingly powerful platform for molecular syntheses, enabling applications to natural product syntheses, late-stage modification, pharmaceutical industries and material sciences, among others. This Primer summarizes representative best practices for the experimental set-up and data deposition for C–H activation, as well as discussing key developments including recent advances in asymmetric, photoinduced and electrocatalytic C–H activation. Likewise, strategies for applications of C–H activation towards the assembly of structurally complex (bio)polymers and drugs in academia and industry are discussed. In addition, current limitations in C–H activation and possible approaches for overcoming these shortcomings are reviewed.