We discuss our recent efforts in the design and architectural control of titania nanostructures and their applications.We first review the synthesis, crystallinity control, and photocatalysis of TiO2 porous nanostructures by discussing several methods for changing the structures ~om amorphous to crystalline and subsequently ways for enhancing the crystallinity, including those involving the "silica-protected calcination" and "partial etching and re-calcination" strategies.We also discuss the photocatalytic applications of the TiO2 nanoshells and the methods for improving their catalytic activities.In particular, we demonstrate a sandwich-structured photoeatalyst that shows an excellent performance in degradation reactions of a number of organic compounds under UV, visible light, and direct sunlight.