Size, dimensionality, and shape play important roles in determining the properties of nanomaterials. So far, most of the nanomaterial researches have been focused on zero-dimensional nanoparticles/nanodots and one-dimensional nanowires/nanorods/nanotubes, but very few studies have been carried out on two-dimensional nano-sheets. Starting from carbon, recently we have succeeded in growing a class of nanostructured two-dimensional materials either in the pure forms or in the form of composites with carbon. In this paper, we will first briefly discuss various types of two-dimensional systems and then focus on the formation mechanism of carbon nanowalls and their field-emission and electron transport properties. The use of carbon nanowalls as templates for the formation of other types of nanomaterials will also be discussed.