This is a Christmas card sent by John Lennon and Yoko Ono in 1969 to Karlheinz Stockhausen, a avant-garde German composer who was a pioneer in the field of electronic music. Stockhausen was a particular inspiration to Beatles, and his work Hymnen is said to have influenced Lennon to create "Revolution #9" for the white album. He is one of the figures pictured on the cover of Sgt. Pepper's Lonely Hearts Club Band. (He's in the top row, just to the left of W. C. Fields.) Because Lennon personalized the card, I'm showing not just the front but also the inside and back.
Collection of Stockhausen Foundation for Music, Germany