1100 (MC) was a leap year starting on Sunday of the Julian calendar, the 1100th year of the Common Era (CE) and Anno Domini (AD) designations, the 100th year of the 2nd millennium, the 100th and last year of the 11th century, and the 1st year of the 1100s decade. As of the start of 1100, the Gregorian calendar was 6 days ahead of the Julian calendar, which was the dominant calendar of the time.

• August 5 – Henry I crowned King of England in Westminster Abbey

• May 23 – Emperor Qinzong of China (d. 1161)
• Mary and Eliza Chulkhurst, English conjoined twins (died 1134)
• Gilbert de Clare, 1st Earl of Pembroke (died 1148)

• August 2 – William II of England