CSIO may refer to:
Central Scientific Instruments Organisation, an Indian national laboratory dedicated to research, design and development of scientific and industrial instruments Centre for Study of Insurance Operations, the Canadian property and casualty insurance industry's nonprofit association of insurers, brokers and software providers City State of the Invincible Overlord, a 1976 Judges Guild product that was the first published fantasy role-playing game city setting Concours de Saut International Officiel, a ranking system for the equestrian competition show jumping