The book covers a variety of studies of organic semiconductors‎,‎ from fundamental electronic states to device applications‎,‎ including theoretical studies‎.‎ Furthermore‎,‎ innovative experimental techniques‎,‎ e‎.‎g‎.‎‎,‎ ultrahigh sensitivity photoelectron spectroscopy‎,‎ photoelectron yield spectroscopy‎,‎ spin‎-resolved scanning tunneling microscopy ‎(‎STM‎)‎‎,‎ and a material processing method with optical‎-vortex and polarization‎-vortex lasers‎,‎ are introduced‎.‎ As this book is intended to serve as a textbook for a graduate level course or as reference material for researchers in organic electronics and nanoscience from electronic states‎,‎ fundamental science that is necessary to understand the research is described‎.‎ It does not duplicate the books already written on organic electronics‎,‎ but focuses mainly on electronic properties that arise from the nature of organic semiconductors ‎(‎molecular solids‎)‎‎.‎ The new experimental methods introduced in this book are applicable to various materials ‎(‎e‎.‎g‎.‎‎,‎ metals‎,‎ inorganic and organic materials‎)‎‎.‎ Thus the book is als‎.‎‎.‎‎.‎