From a chemistry aspect, graphene is the extrapolated extreme of condensed polycyclic hydrocarbon molecules to infinite size. Here, the concept on aromaticity which organic chemists utilize is applicable. Interesting issues appearing between physics and chemistry are pronounced in nano-sized graphene (nanographene), as we recognize the importance of the shape of nanographene in understanding its electronic structure. In this book, the fundamental issues on the electronic, magnetic, and chemical properties of condensed polycyclic hyodrocarbon molecules, nanographene and graphene are comprehensively discussed.