**5. Conclusions**

The surface structure of TiO2 is constantly being recognized as a crucial factor regarding its photocatalytic activity. Control over this interface can be achieved by exposing the specific crystal facets, which allows detailed insight into the reaction kinetics and mechanism. Experimentally, such high-quality structures can be prepared through energetic stabilization of the specific facet, with simultaneous control of nucleation and growth rates. However, contrary to the preparation procedures, surface energy is now recognized as a less important factor for the final photocatalytic activity. Here, more attention is given to the electronic properties, detailed interactions with substrates, and local defects. However, as the presented chapter aimed to provide a general introduction to the problem of TiO2 facets, only some of the recent findings were stressed here, while these problems are still under constant intensive research. Particularly, it should be highlighted that further modifications and charge separation between different co-exposed facets are now used to achieve remarkable final photocatalytic efficiency of different materials. In this regard, we believe that the presented findings will be useful for further studies in this direction, providing a survey of different aspects of crystal facet engineering of TiO2, a photocatalyst that is still the most studied in this field.
