- YSI stands for Yousendit (File Transfer Website)
- YSI stands for Young Sustainable Impact (Norway)
- YSI stands for Youth Service, Inc. (Philadelphia, PA)
- YSI stands for Yellow Springs Instruments (Yellow Springs, OH)
- YSI stands for You Said It
- YSI stands for Young Social Innovators (Ireland)
- YSI stands for Youth Science Institute
- YSI stands for Young Scots for Independence (Edinburgh, Scotland, UK)
- YSI stands for Youth Sports Institute (various locations)
- YSI stands for You Stupid Idiot
YSI