Atomic layer deposition ( ALD ) is a cyclic process which relies on sequential self-terminating reactions between gas phase precursor molecules and a solid surface. The self-limiting nature of the chemical reactions ensures precise film thickness control and excellent step coverage, even on 3D structures with large aspect ratios. At present, ALD is mainly used in the microelectronics industry, e.g. for growing gate oxides . The excellent conformality that can be achieved with ALD also renders it a promising candidate for coating porous structures, e.g. for functionalization of large surface area substrates for catalysis, fuel cells, batteries, supercapacitors, filtration devices, sensors, membranesetc. This tutorial review focuses on the application of ALD for catalyst design. Examples are discussed where ALD of TiO₂ is used for tailoring the interior surface of nanoporous films with pore sizes of 4–6 nm, resulting in photocatalytic activity. In still narrower pores, the ability to deposit chemical elements can be exploited to generate catalytic sites. In zeolites , ALD of aluminium species enables the generation of acid catalytic activity.