Nanoporous graphene (NPG) materials enjoy the high electrochemical stability, high electrical conductivity, and flexibility of the continuous three-dimensional (3D) graphene architecture, with high surface area and nanoporosity. NPGs are synthesized by (i) chemical vapor deposition (CVD) of methane (CH4) using nanoparticles of non-transition-metal oxides such as γ-alumina (γ-Al2O3) and MgO 8 as the template, (ii) the subsequent acid etching for removing the metal oxides, and (iii) the annealing of the obtained nanoporous carbon (NPC) materials to give the 3D continuous architecture (Fig. ). The mechanism of the initial NPCs formation at the early-stage CH4-CVD reactions has been well-documented based on the reaction kinetics and quantum chemistry. The use of relatively inert CH4 as the gaseous carbon source is crucial for kinetically achieving the formation of mono-layered carbon. We also revealed that the thermal treatment of NPCs at high temperatures under an inert atmosphere affords the corresponding NPGs by fusing the H-terminated edges, and this is the origin of the electrochemical stability of NPGs. This annealing following the CH4-CVD synthesis will also improve the integrity of the graphene architecture by reducing the defect concentration, which is helpful to develop stable electrochemical devices using NPGs such as long-lived air-metal batteries etc. The quantitative evaluation of the defect type and concentration before/after annealing will be a starting point for the development of state-of-the-art continuous porous carbon materials based on NPGs chemistry, but recent investigations on the structural changes upon annealing by changing the size of templates gave us a qualitative picture.