Methods for selective C-H bond functionalization have provided chemists with versatile and powerful toolboxes for synthesis, such as the late-stage modification of a lead compound without the need for lengthy de novo synthesis(1-5). Cleavage of an sp(3) C-H bond via hydrogen atom transfer (HAT) is particularly useful, given the large number of available HAT acceptors and the diversity of reaction pathways available to the resulting radical intermediate(6-17). Site-selectivity, however, remains a formidable challenge, especially among sp(3) C-H bonds with comparable properties. If the intermediate radical could be further trapped enantioselectively, this should enable highly site- and enantioselective functionalization of C-H bonds. Here we report a copper (Cu)-catalysed site- and enantioselective allylic C-H cyanation of complex alkenes, in which a Cu(ii)-bound nitrogen (N)-centred radical plays the key role in achieving precise site-specific HAT. This method is shown to be effective for a diverse collection of alkene-containing molecules, including sterically demanding structures and complex natural products and pharmaceuticals.