Engineered nanomaterials (ENMs) have greatly impacted human society as well as natural environments over the past decade, in consequence of their production on a massive scale to support the emerging market for nanotechnology. Among these ENMs, titanium dioxide (TiO2) nanoparticles have been extensively employed in the development of novel solutions for photocatalytic applications in environmental remediation. This book discusses the fate of TiO2 and the effects in natural environments. Some other topics discussed include indoor environment control with functional mortars; the production, properties and applications of TiO2; dye-sensitized TiO2 for gas detection; TiO2 induced photocatalytic reduction for organic synthesis; and the effects of TiO2 nanoparticles on the inflammatory process.