Atomic layer deposition (ALD) of TiO2 thin films on a Si substrate has been investigated using titanium isopropoxide (TTIP) and tetrakis(dimethylamino)titanium (TDMAT) in combination with water. The deposition rate and the chemical stability of the films are significantly different depending on the Ti precursor and process temperature (TALD). When the films are annealed a significant thickness shrinkage is reported for the first time on TiO2. A comprehensive analysis of the films with X-ray photoelectron spectroscopy, Fourier transform infrared, ellipsometry, and porosimetry demonstrates that some precursor ligands are incorporated (most likely as isopropanol) when ALD is performed at low temperature (i.e., TALD < 200 °C) using TTIP. The trapped ligand molecules can be removed by annealing but make the film porous and thus have a detrimental effect on the dielectric properties. Higher-quality nonporous films are grown by using TTIP at TALD ≥ 200 °C or by using TDMAT. It is shown that measuring the refractive index is a simple, nondestructive, and reliable way to determine film quality. Numerical simulations of ligand coverage show that the measured growth rates are consistent with a self-limiting ALD mechanism albeit with partial incorporation of ligands from TTIP at low temperature (TALD < 200 °C), which renders part of the surface inactive toward growth. Aside from this, the higher growth rate of TDMAT is due to more desorption of ligands during the Ti precursor pulse. The overall decrease in the growth rate with temperature is related quantitatively to decreasing coverage of hydroxyl groups on TiO2. Comparing the TTIP and TDMAT processes in this way reveals new aspects of the gas-surface chemistry during self-limiting ALD and how this affects film morphology and electrical properties.