Christmas

Christmas was a traditional holiday celebrated by many Humans on Earth. It evolved from a number of religious and secular festivals over several millennia and eventually came to be widely recognized as a holiday celebrating the birth of ancient religious leader Jesus Christ, although it was also widely celebrated secularly.

History
Although he is an alien, the Doctor has developed a fondness and appreciation for the celebration of Christmas. Christmas celebrations existed in as far away a time and place at the planet Puxatornee in the year 3090. (BFA: Flip-Flop) Even the normally serious Sara Kingdom from the year 4000 celebrated the holiday with the Doctor's first incarnation. (DW: The Daleks' Master Plan)

The Doctor, jokingly or otherwise, claimed to have left Rose Tyler a red bicycle she wanted for Christmas many years before (from her perspective) they first met. (DW: The Doctor Dances)

The Tenth Doctor claimed in The Voyage of the Dammed that he was there for the very first christmas. He stated in The Satan Pit that he doesn't believe in any god, so there for in the Doctor Who universe, Christmas is not a celebration of the birth of Jesus Christ.

Christmas activities in England include pantomime. At a UNIT Christmas party, the Doctor, Jo Grant and others put on a production of Aladdin. (NA: Timewyrm: Revelation, No Future)

Earth -- and, specifically the vicinity of London -- experienced a number of major events involving aliens at or around Christmas Day starting in the early 21st century. In 2006, Christmas coincided with the arrival of the Guinevere One space probe at Mars, but this celebration was disrupted by the subsequent Sycorax invasion; this event was later cited by the Doctor as the moment the people of Earth were irrevocably introduced to the idea of alien life (after years of isolated and covered-up incidents) (DW: The Christmas Invasion); this event also had personal significance to the Doctor as he experienced it immediately after regenerating into his tenth incarnation. In 2007, the arrival of the Webstar over London panicked the populace. (DW: The Runaway Bride). For Christmas 2008, the populace of London (except a few holdouts such as Queen Elizabeth II and Wilfred Mott) voluntarily evacuated the city in case of another alien invasion (no invasion occurred, but a spaceship replica of The Titanic nearly crashed into Buckingham Palace). (DW: Voyage of the Damned).

Other Christmastime incidents have included a Christmas Eve attempt by the Gelth to come through the Cardiff Rift in 1869 (DW: The Unquiet Dead). Apparently some incident occurred in San Francisco at Christmas in the year 2000, but the details are not known. (DW: Doctor Who: The TV Movie)

In many Earth cultures, the "Christmas season" or "Holiday season" usually continues until the turning of the new year, which occurs six days later. Several events of note occurred on December 31, 1999, otherwise known as New Year's Eve, including the Doctor successfully thwarting an attempt by the Master to steal his remaining regenerations, soon after the Doctor had himself regenerated (DW: Doctor Who: The TV Movie); and the staff of Torchwood 3 being murdered, leaving Jack Harkness in charge (TW: Fragments). This latter event occurred as the Torchwood Hub still had Christmas decorations on display.

Alternate timeline
In the alternate timeline experienced by Donna Noble due to the manipulations of the Trickster, the Doctor died during the incident with the Webstar at Christmas 2007, while the Titanic replica crashed into London at Christmas 2008, destroying the city and flooding most of southern England with radiation, sparking a chain of events leading to the country becoming a police state. This timeline was subsequently negated. (DW: Turn Left)

Doctor Who

 * "The Feast of Steven," episode 7 of The Daleks' Master Plan
 * The Unquiet Dead
 * The Christmas Invasion
 * The Runaway Bride
 * Voyage of the Damned
 * Turn Left (partially)
 * The Next Doctor

Torchwood

 * Out of Time

K-9 & Company

 * A Girl's Best Friend

Comics

 * A Christmas Story

Novels

 * Nightshade
 * Christmas on a Rational Planet
 * Damaged Goods

Short Story anthologies

 * Short Trips: A Christmas Treasury
 * Short Trips: The History of Christmas
 * Short Trips: Ghosts of Christmas

Other short fiction

 * Prelude: Conundrum
 * Deep and Dreamless Sleep
 * The Hopes and Fears of All the Years

Audio

 * The Chimes of Midnight
 * The One Doctor (In an extra scene, the Doctor and Mel watch the Queen's speech)
 * Flip-Flop