1990 (MCMXC) was a common year starting on Monday of the Gregorian calendar, the 1990th year of the Common Era (CE) and Anno Domini (AD) designations, the 990th year of the 2nd millennium, the 90th year of the 20th century, and the 1st year of the 1990s decade. September 14, 1990 saw the first case of successful somatic gene therapy on a patient. Encyclopædia Britannica, which ceased printing in 2012, saw its highest all time sales in 1990; 120,000 volumes were sold that year.