Meeting the world’s growing energy needs sustainably is one of the most important challenges of our time, and electrochemical devices such as fuel cells and batteries will continue to hold a significant place in sustainable energy systems. Due to the central role that interfaces have in electrochemical systems, it is critical to engineer and control these interfaces. This talk will describe our research on layer-by-layer synthetic strategies, namely atomic layer deposition (ALD), to engineer thin film materials used at electrochemical interfaces with a high level of control over composition, structure, and thickness. Both battery and electrocatalysis applications for energy storage and conversion will be described. We use ALD interfacial layers deposited on the copper current collector as a new strategy to control lithium metal morphology and improve electrochemical performance in Li metal batteries. Specifically, TiO₂ films deposited by ALD on the current collector of lithium anodes generate a lithiophilic surface layer that enables uniform and reversible Li plating, leading in turn to improvements in battery cyclability. Other metal oxide interfacial layers are also shown to influence lithium morphology and battery performance. Toward electrocatalysis, we show that nanometer thick layers of earth abundant materials deposited by ALD are active for the oxygen evolution reaction (OER), an important reaction in the conversion of sunlight to fuels. Nickel-oxide, nickel-iron-oxide, and nickel-aluminum-oxide films are synthesized with controlled composition by ALD and the promotion of the OER activity by iron and aluminum is explored. The potential of atomic layer deposition to synthesize nanoscale materials and engineer interfaces for electrochemical energy applications will be discussed.