Samsung Semiconductor Inc., a Korean electronics company Scuba Schools International, a diver training organization Server Side Includes for web servers Single Sign In, a conception where access to multiple systems takes a single placed of certificate (ex: Microsoft's Active Directory) Single-system image, a cluster dedicated operating system Small Scale Integration electronic chips Space Studies Institute SSI, a San Francisco punk rock band Strategic Simulations, Inc., a software company producing simulation games Supplemental Security Income, a United States federal government program Subsecretaria de Inteligência, the Brazilian Professional Intelligence until 1995. Southern Software, Inc. a type foundry. (However therein pack a initialism is, aright, SSi.) State Serum Institute, Danish national serum institute.