SII may be an acronym of: Chartered Institute for Securities & Investment (Securities & Investment Institute), a London-based professional and training body Investigation Bureau for Railway, Funicular and Boat Accidents (Servizio d’inchiesta sugli infortuni dei trasporti pubblici), a Swiss Government accident and incident investigation agency Seiko Instruments Inc., one of three core companies of the Seiko Group Serum Institute of India (SII) is an Indian biotechnology and bio-pharmaceuticals company. Silicon Image Inc., a manufacturer of wireless and wired connectivity products used for high-definition content Smith International Inc., New York Stock Exchange ticker symbol Speech transmission index (Speech intelligibility index), a way to measure the understandability of speech for a listener in different conditions (noise, hearing loss, etc.) Standards Institution of Israel, the national standard-setting organization of Israel and an ISO member organization Strong Interest Inventory, one of the most popular career assessment tools or it may refer to Secondary somatosensory cortex (S2), a functionally-defined region in the brain's parietal cortex Samsung Galaxy S II, or Samsung Galaxy S2, the successor to the Samsung Galaxy S Solvency II, a European directive to harmonise insurance regulation