Graphdiyne (GDY) is a flat material comprising sp2- and sp-hybridized carbon atoms with high degrees of π conjugation that features uniformly distributed pores. It is interesting not only from a structural point of view but also from the perspective of its electronic, chemical, mechanical, and magnetic properties. We have developed an in situ homocoupling reaction of hexaethynylbenzene on Cu foil for the fabrication of large-area ordered films of graphdiyne. These films are uniform and composed of graphdiyne multilayers. The conductivity of graphdiyne films, calculated at 2.52 × 10-4 S m-1, is comparable to that of Si, suggesting excellent semiconducting properties. Through morphology-controlled syntheses, we have prepared several well-defined graphdiyne structures (e.g., nanotubes, nanowires, and nanowalls) having distinct properties. The graphdiyne nanotube arrays and graphdiyne nanowalls exhibited excellent field emission performance, higher than that of some other semiconductors such as graphite and carbon nanotubes. These structures have several promising applications, for example, as energy storage materials and as anode materials in batteries. The unique atomic arrangement and electronic structure of graphdiyne also inspired us to use it to develop highly efficient catalysts; indeed, its low reduction potential and highly conjugated electronic structure allow graphdiyne to be used as a reducing agent and stabilizer for the electroless deposition of highly dispersed and surfactant-free Pd clusters. GDY-based three-dimensional (3D) nanoarchitectures featuring well-defined porous network structures can function as highly active cathodes for H2 evolution. Heteroatom-doped GDY structures are excellent metal-free electrocatalysts for the oxygen reduction reaction (ORR). Its excellent electrocatalytic activity and inexpensive, convenient, and scalable preparation make GDY a promising candidate for practical and efficient energy applications; indeed, we have explored the application of GDY as a highly efficient lithium storage material and have elucidated the method through which lithium storage occurs in multilayer GDY. Lithium-ion batteries featuring GDY-based electrodes display excellent electrochemical performance, including high specific capacity, outstanding rate performance, and long cycle life. We have also explored the application of GDY in energy conversion and found that it exhibits excellent conductivity. In this Account, we summarize the relationships between the functions of graphdiyne and its well-defined nanostructures. Our results suggest that GDY is a novel 2D carbon material possessing many attractive properties. It can be designed into new nanostructures and materials across a range of compositions, sizes, shapes, and functionalities and can be applied in the fields of electronics, optics, energy, and optoelectronics.