Recent discovery of topological insulators highlighted a new class of quantum phases, namely topological phases, characterized by exotic surface states and quantized response functions. While topological insulators are well understood, topological aspects of metals are less clear. In this talk, I’ll discuss a class of electronic topological semimetals, which are 3d analogies of graphene. They are solid state realizations of Weyl fermions, hence coined Weyl semimetals. I’ll discuss their topological properties, including surface Fermi arcs and bulk quantum Hall effects. In the presence of electronic interactions, charge density wave and superconductivity can develop in Weyl semimetals. I’ll show that these symmetry breaking states inherit the nontrivial topology from Weyl semimetals.