Atomic layer deposition (ALD) frequently produces amorphous films, however crystalline phases are often desired for various electrical, chemical, and optical applications. Thus, understanding the fundamental crystallization kinetics of films deposited by ALD is important in designing process pathways to achieve low-temperature crystallization, ultra-thin film (<50 nm) crystallization, controlled microstructures, and epitaxial growth. This presentation will discuss our work to study the crystallization kinetics in ALD TiO₂ thin films and challenge some pre-conceived notions about thickness and temperature requirements for ALD film crystallization. We will focus on a prototypical TiO₂ ALD process using tetrakis(dimethylamino)titanium(IV) (TDMAT) and water at between 140 °C and 220 °C. Initially, we will discuss data collected on post-deposition, isothermal crystallization kinetics at temperatures ranging from 140 to 200 °C. These time-dependent transformation kinetics are fit to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, revealing a continuous nucleation process and a two-dimensional growth mechanism, consistent with the observed grain sizes. We also use images collected over short annealing times to independently determine the crystal nucleation rate, which allows us to determine that the activation energies for nucleation (1.32–1.35 eV K^-1 atom^-1) are about one order of magnitude greater than the activation energies for grain growth (0.12–0.24 eV K^-1 atom^-1), sugggesting that nucleation is the more significant barrier to crystallization in this system. Finally, we will show how a modification to the process’s chemical environment can lower this barrier to nucleation leading to dramatic in situ crystallization (with no post-deposition annealing) at unusually low process temperatures and film thicknesses (< 15 nm).