III-nitride compound semiconductors (AlN, GaN, InN) and their alloys have emerged as versatile and high-performance materials for a wide range of electronic and optoelectronic device applications. Although high quality III-nitride thin films can be grown at high temperatures (>1000 °C) with significant rates, deposition of these films on temperature-sensitive device layers and substrates necessitates the adaptation of low-temperature methods such as atomic layer deposition (ALD). When compared to other low-temperature thin film deposition techniques, ALD stands out with its self-limiting growth mechanism, which enables the deposition of highly uniform and conformal thin films with sub-angstrom thickness control. These unique characteristics make ALD a powerful method especially for depositing films on nanostructured templates, as well as preparing alloy thin films with well-defined compositions. This monograph reports on the development of low-temperature (≤200 °C) plasma-assisted ALD processes for III-nitrides, and presents detailed characterization results for the deposited thin films and fabricated nanostructures.