In 1910 Ivar Bang reported that concentrated solutions of guanylic acid formed a gel. It took half a century before Gellert et al. in 1962 discovered the structural motif, a guanine-quartet, to be the basis for guanylic acid gelation. This chapter starts with a historical overview and gives credit to Ivar Bang and several other pioneers in the field. Then the basic principles of guanine self-assembly are explored, either for individual molecules like guanosine and its derivatives, or for guanine-rich oligonucleotides and G-rich DNA-sequences. Finally, we show how these guanine-based nanoarchitectures are visualised by surface techniques like scanning tunnelling microscopy or atomic force microscopy.