Heterojunction, the interface between two dissimilar crystalline materials, has been one of ideal platforms for the two-dimensional electronic systems (2DES). Examples include the quantum Hall effect which was first observed in the semiconductor heterostructures. Recently, a heterostructure made from two transition metal oxides LaTiO3 and SrTiO3 has opened a new door for us to engineer the physical properties of transition metal oxides. In particular, since many of the transition metal oxides are strongly correlated materials, new types of 2DES with strong correlation could emerge from these new oxide interfaces. In this talk, I will first introduce the experimental and theoretical developments in this new field. Then I will present our model to study the Mott-insulator heterostructure and demonstrate our proposal to create novel 2D doped Mott insulators from it.