Broke many of the rules prevalent for animated holiday specials during the 1960s: it didn't make use of a laugh track; real children were used for the character voices instead of adult actors imitating children's voices; and Biblical references were used to illustrate the true meaning of Christmas.
Kathy Steinberg, who did the voice of Sally Brown, had not yet learned to read at the time of production, so she had to be fed her lines, often a word or syllable at a time, which explains the rather choppy delivery of the line "All I want is what I have coming to me. All I want is my fair share".
When viewing the rough cut of the show, both Bill Melendez and Lee Mendelson were convinced that they had a flop on their hands. After it premiered, they were happily surprised and shocked at the high ratings and excellent reviews that the show received. Today, the show remains the second longest-running Christmas special on US network television (the 1964 Rudolph the Red-Nosed Reindeer (1964) premiered one year earlier and is still broadcast every year on US network television).
Just before her remarks about Christmas being a big commercial racket, Lucy refers to Charlie Brown simply as Charlie. This is the only time she does this in any of the TV specials: every other time it's Charlie Brown.
When they first saw the show, CBS executives were horrified at the idea of an animated Christmas special with such a blatant message. They also strongly objected to the fact that the show had no canned laughter. In addition, they greeted Vince Guaraldi's jazz score as an intrusion in the special that audiences would never accept. However, when CBS learned to their astonishment of the special's spectacular ratings earned on its initial broadcast and the glowing reviews for it, the network promptly contracted the producers for more specials.
The original broadcast included some brief animated sections which included the logo of Coca-Cola, the show's original sponsor. These have been edited out of subsequent broadcasts and the video release. Right after the opening title, Linus crashed into a sign advertising Coca-Cola after being tossed by Snoopy. (Look at current versions and you'll notice that we never see where Linus lands!) The closing carol originally included the complete verse (instead of fading out) with a final on-screen "Merry Christmas from your local bottler of Coca-Cola" right after the United Feature Syndicate credit at the end.
The version of the show broadcast on CBS-TV until 1997 and older video releases are edited: they leave out a scene where the gang throws snowballs at a can on a fence. The Paramount and Warner video releases are complete and unedited.
Patty in this special is not Patricia "Peppermint Patty" Reichardt. The latter first appeared several years later in the strip. The former was phased out gradually, disappearing completely by the end of the 1970s, despite being one of the four original Peanuts characters.
The idea was given by John Allen, who worked for an ad agency for Coca-Cola, as he called Lee Mendelson. He originally saw the documentary that was cancelled to be broadcast, because he was unable to sell it. He asked Mendelson if the producers of "Peanuts" thought about making a Christmas special. Allen also expected the plot to be given only in a four day period, but was able to manage this.
Over the decades, with American TV networks making more broadcast time for commercials, this special was increasingly cut for time until there was a storm of protest from fans. When the special was acquired by the ABC TV network, a compromise was reached to both answer those complaints and to take advantage of the opportunity to sell more advertising time for a reliably high-rated annual rerun. This consisted of broadcasting an uncut version of the special in an hour timeslot, and using the remaining time after the special to run a companion piece, Charlie Brown's Christmas Tales (2002).
The trivia items below may give away important plot points.
Bill Melendez tried to talk Charles M. Schulz out of using Biblical references (especially Linus's speech) in this special. Schulz reportedly won him over by saying, "If we don't do it, who will?" As it turned out, Linus' recitation was hailed as one of the most powerful moments in the highly acclaimed special.
During his famed speech, Linus, who is well known to be dependent on his security blanket, actually lets go of it when he recites these words: "Fear not: for, behold, I bring you good tidings of great joy," which is from Luke 2:10.