Two-dimensional van der Waals materials such as transition metal dichalcogenides (TMDs) can be seen as a new class of quantum wells on the atomic level, where quantum mechanics plays an important role. Similar to III-V semiconductors, monolayer TMDs are direct bandgap materials and can emit light efficiently. These bandgaps are located at the corner of the Brillion zone, forming multiple energy-degenerate but quantum mechanically distinct valleys, which resembles the spin degree of freedom in many regards. On the other hand, unlike traditional quantum wells, 2D materials do not require epitaxial growth on single crystalline substrates with high dielectric constant, which significantly reduces the screening of Coulomb interaction between electrons. As a result, a variety of tightly bound excitons can exist in atomically thin TMDs. In this talk, I will give an overview of these valley excitons and discuss how to control them with tools such as ultrafast light. In addition, I will also talk about our progress at UBC in exploring new physics enabled by van der Waals heterostructures with and without twists.