<p>Atomic layer deposition (ALD) is a surface-controlled chemical vapour deposition method, in which materials are prepared one atomic layer at the time. With ALD, film thickness can be controlled very precisely, and it allows the user to cover large areas and surfaces with a complex three-dimensional structure uniformly and conformally. ALD is used for the deposition of high-quality thin films and nanostructures, as well as for surface functionalization and interface engineering in a wide range of applications, both from a research and development perspective, as well as for high-volume manufacturing. This Primer outlines the method of ALD, describing the precursors, coreactants and tools commonly used and illustrating examples of typical results from ALD processes. We describe the implementation of ALD in high-volume manufacturing in the semiconductor, solar and display industry and detail other existing and emerging application fields. We devote special attention to the reproducibility of the method, key technical specifications and figures of merit, as well as its limitations and challenges. Finally, we outline the future perspective of ALD and its applications to position it within the broader trend of atomic-scale processing.</p>