Holy days
Memorial of Christ's Death
The most important religious event of the year for Jehovah's Witnesses is the commemoration of the Memorial of Christ's Death, which takes place on the anniversary of the Last Supper, calculated according to the lunar calendar in use in Christ's time. They believe that this is the only observance commanded by Christ.
Christian festivals
Witnesses do not celebrate Christmas or Easter because they believe that these festivals are based on (or massively contaminated by) pagan customs and religions. They point out that Jesus did not ask his followers to mark his birthday.
Secular festivals
Witnesses do not celebrate birthdays or other secular festivals that originate in other religions.