Original: Although Ukraine was one of the three founding countries and ratified the Creation Agreement in December 1991, Ukraine did not choose to ratify the CIS Charter and is not a member of the CIS.
Simplified: Before joining the CIS, on 21st December 1991, leaders of these 11 countries had met in Kazakhstan to accept the original CIS agreement of 8th December 1991. In December 1993, Georgia also joined the CIS.