1966

January

 * 1 - The TARDIS departs Trafalgar Square, where it had arrived during the New Year's Eve celebrations. (DW: The Daleks' Master Plan)

July

 * 5 - Ben Jackson begins a five month shore posting. (DW: The War Machines)
 * 12 through 20 - From its base in the Post Office Tower in London, WOTAN directs both mind controlled Humans and robot War Machines. (DW: The War Machines)
 * 20 - The Doctor, Polly, Ben Jackson and Jamie McCrimmon get involved with the schemes of the Chameleons at Gatwick Airport. Ben and Polly decide to stay behind in their own time. (DW: The Faceless Ones) Meanwhile, the Daleks steal the Doctor's TARDIS. (DW: The Evil of the Daleks)

November

 * 15 - Birth of Peri Brown, companion of the Doctor in his fifth and sixth incarnations. (DW: Planet of Fire)

Unknown date

 * The Doctor's TARDIS and the DARDIS materialise on an observation deck of the Empire State Building. (DW: The Chase)
 * The Doctor and Rose Tyler visit London. (DWM: The Love Invasion)
 * Ace and Hex meet Peri Brown and Erimem. (BFA: The Veiled Leopard)

January

 * 01 - "Volcano" (DW: The Daleks' Master Plan Episode 8) is first broadcast.
 * 08 - "Golden Death" (DW: The Daleks' Master Plan Episode 9) is first broadcast.
 * 15 - "Escape Switch" (DW: The Daleks' Master Plan Episode 10) is first broadcast.
 * 22 - "The Abandoned Planet" (DW: The Daleks' Master Plan Episode 11) is first broadcast.
 * 29 - "Destruction of Time" (DW: The Daleks' Master Plan Episode 12) is first broadcast. Jean Marsh leaves the series as her character, Sara Kingdom, becomes the second companion to die in the line of duty.
 * 30 - Daphne Ashbrook is born in Long Beach, California.

February

 * 05 - "War of God" (DW: The Massacre of St Bartholomew's Eve Episode 1) is first broadcast.
 * 12 - "The Sea Beggar" (DW: The Massacre of St Bartholomew's Eve Episode 2) is first broadcast.
 * 19 - "Priest of Death" (DW: The Massacre of St Bartholomew's Eve Episode 3) is first broadcast.
 * 26 - "Bell of Doom" (DW: The Massacre of St Bartholomew's Eve Episode 4) is first broadcast. Jackie Lane makes her debut as companion Dodo Chaplet.

Early 1966

 * Exact date unknown - William Hartnell sends shockwaves through the Doctor Who production team by announcing his intention to leave the series. Over the coming months producers and writers develop the concept of regeneration to explain the change of lead actor and cast Patrick Troughton as the new Doctor; Hartnell eventually agrees to appear in the first two serials of the new season.

March

 * Publication of Dalek Action Paint 'n Puzzle by Souvenir Press.
 * Publication of Dr. Who Travels in Space Sticker Fun Book.
 * Publication of Dr. Who Travels in Time Sticker Fun Book.
 * 05 - "The Steel Sky" (DW: The Ark Episode 1) is first broadcast.
 * 12 - "The Plague" (DW: The Ark Episode 2) is first broadcast.
 * 19 - "The Return" (DW: The Ark Episode 3) is first broadcast.
 * 26 - "The Bomb" (DW: The Ark Episode 4) is first broadcast.

April

 * Century 21 Records releases a Doctor Who edition of its 21 Minutes of Adventure LP record series, featuring the audio soundtrack of "The Planet of Decision", a chapter of DW: The Chase. It is the first audio story to be made available for sale.
 * 02 - "The Celestial Toyroom" (DW: The Celestial Toymaker Episode 1) is first broadcast.
 * 09 - "The Hall of Dolls" (DW: The Celestial Toymaker Episode 2) is first broadcast.
 * 16 - "The Dancing Floor" (DW: The Celestial Toymaker Episode 3) is first broadcast.
 * 23 - "The Final Test" (DW: The Celestial Toymaker Episode 4) is first broadcast.
 * 30 - "A Holiday for the Doctor" (DW: The Gunfighters Episode 1) is first broadcast.

May

 * The Doctor Who production office circulates a memo to writers outlining the proposed character of the Second Doctor, as well as suggestions as to how to handle the first regeneration, which is initially compared to an LSD trip gone bad.
 * 07 - "Don't Shoot the Pianist" (DW: The Gunfighters Episode 2) is first broadcast.
 * 14 - "Johnny Ringo" (DW: The Gunfighters Episode 3) is first broadcast.
 * 21 - "The OK Corral" (DW: The Gunfighters Episode 4) is first broadcast. This marks the final time individual episode titles would be used in the original series (the practice would resume in 2005).
 * 28 - DW: The Savages Episode 1 is first broadcast.

June

 * 04 - DW: The Savages Episode 2 is first broadcast.
 * 11 - DW: The Savages Episode 3 is first broadcast.
 * 18 - DW: The Savages Episode 4 is first broadcast. Peter Purves leaves the series with this episode, although he would continue his association with Doctor Who for years to come when he subsequently becomes co-host of Blue Peter, often presenting promotional features about the series.
 * 25 - DW: The War Machines Episode 1 is first broadcast. Michael Craze and Anneke Wills make their debuts as Ben Jackson and Polly, respectively. This episode is notorious for having a character -- the computer WOTAN -- break the longstanding taboo of referring to the Doctor by the name "Doctor Who".

July

 * 02 - DW: The War Machines episode 2 is first broadcast. Final appearance of Jackie Lane as Dodo Chaplet.
 * 09 - DW: The War Machines Episode 3 is first broadcast.
 * 16 - DW: The War Machines Episode 4 is first broadcast, concluding the third season.
 * The film Dr. Who and the Daleks is released to theatres in the United States. For most audiences in America, this is their first exposure to the Doctor Who concept, as the TV series has not as of this date been broadcast in the US (although some communities bordering Canada have been able to view the series on the CBC network).

August

 * 05 - The second feature film, Daleks - Invasion Earth 2150 AD, based upon DW: The Dalek Invasion of Earth, is released in the UK.

September

 * Publication of the second Doctor Who Annual.
 * 8 - The Dalek Outer Space Book is first published.
 * Star Trek debuts in America. This influential series would go on to become Doctor Who's chief rival in terms of franchise longevity, although the original series would only run until the spring of 1969.
 * 10 - DW: The Smugglers Episode 1 is first broadcast, marking the beginning of Season 4.
 * 17 - DW: The Smugglers Episode 2 is first broadcast.
 * 24 - DW: The Smugglers Episode 3 is first broadcast.

October

 * 01 - DW: The Smugglers Episode 4 is first broadcast.
 * 08 - DW: The Tenth Planet Episode 1 is first broadcast, marking the first appearance of the Cybermen.
 * Episode 4 of DW: The Tenth Planet is taped, with the first scenes filmed being the regeneration from William Hartnell (making his final regular appearance as the First Doctor) to Patrick Troughton (making his first appearance as the Second Doctor).
 * Camille Coduri who plays Jackie Tyler in series 1, 2 and (as a one off appearance) 4 of the revived Doctor Who is born in Wandsworth London.
 * 15 - DW: The Tenth Planet Episode 2 is first broadcast.
 * 17 - Mark Gatiss is born.
 * 22 - DW: The Tenth Planet Episode 3 is first broadcast.
 * Episode 1 of DW: The Power of the Daleks is taped; this is the first full episode featuring Patrick Troughton.
 * 29 - DW: The Tenth Planet Episode 4 is first broadcast, ending in the first regeneration, from William Hartnell to Patrick Troughton, an event that shocks children across Britain.

November

 * 05 - DW: The Power of the Daleks Episode 1 is first broadcast. Patrick Troughton's first full episode as the Doctor, although William Hartnell briefly appears as a mirror reflection.
 * 12 - DW: The Power of the Daleks Episode 2 is first broadcast.
 * 19 - DW: The Power of the Daleks Episode 3 is first broadcast.
 * 26 - DW: The Power of the Daleks Episode 4 is first broadcast.

December

 * 03 - DW: The Power of the Daleks Episode 5 is first broadcast.
 * 10 - DW: The Power of the Daleks Episode 6 is first broadcast.
 * 12 - The BBC Audience Research Dept. files an Audience Research Report on DW: The Power of the Daleks Episode 3, reporting that satisfaction in the episode ranked at 44% with response to new Doctor Patrick Troughton being particularly mixed.
 * 15 - Patrick Troughton is interviewed in Radio Times.
 * 17 - DW: The Highlanders Episode 1 is first broadcast. Frazer Hines debuts as new companion Jamie McCrimmon.
 * 24 - DW: The Highlanders Episode 2 is first broadcast.
 * 31 - DW: The Highlanders Episode 3 is first broadcast.

Unknown dates

 * Doctor Who and the Invasion from Space is published by World Distributors. A hardcover novella, this is the first publication of an original long-form text story to feature the Doctor. (Presumably published prior to October as it features the First Doctor.)
 * US comic book publisher Dell Comics issues a single-issue adaptation of the Dr. Who and the Daleks film. This is the first (and, until the early 1980s, only) appearance of a Doctor Who-related comic book in the US.

Reference and Further reading

 * A History of the Universe by Lance Parkin