I decided to make a list of the missing Doctor Who episodes - which are often known as being 'lost in time', aptly...
There are currently 114 missing episodes from 28 serials, including 12 completely missing serials and 45 episodes from 12 serials for Hartnell and 63 episodes from 15 serials for Troughton and the 6-episode Shada - unless you want to count the 11 black and white Pertwee episodes from 3 serials, including one full serial only available in black and white, in which case there are 124 missing episodes from 31 serials including 13 completely missing serials. All of them have surviving footage except for Marco Polo/A Journey to Cathay, Mission to the Unknown and The Massacre of St Bartholomew's Eve/The Massacre, though you could argue that Marco Polo/A Journey to Cathay has footage as the Edge of Destruction/Inside the Spaceship/Beyond the Sun is completely intact...
00:45 in the video shows the only surviving footage we have of Marco Polo/A Journey to Cathay - which is actually from the Brink of Disaster (The Edge of Destruction/Inside the Spaceship/Beyond the Sun).
List of missing episodes
4-episode run of original versions of episodes that survive through An Unearthly Child/100,000 BC/The Tribe of Gum.
Original version of The Dead Planet (part 1 of The Daleks/The Dead Planet/The Mutants) missing: At some point after recording somebody found out that a technical problem had caused backstage voices to be heard on the tape. In early December 1963 it was remounted with a different costume for Susan. The only surviving bit is the cliffhanger - again, not from the original but from episode 2, The Survivors.
8-episode run of original versions of episodes that survive from The Survivors (The Daleks/The Mutants/The Dead Planet) to The Brink of Disaster (The Edge of Destruction/Inside the Spaceship/Beyond the Sun), unless you insist on saying that The Dead Planet survives. If so, it's a complete run of 13 surviving episodes.
6-episode run of missing episodes through Marco Polo/A Journey to Cathay.
19-episode run of surviving episodes from The Sea of Death (The Keys of Marinus/The Sea of Death) to A Change of Identity (The Reign of Terror/The French Revolution).
The Tyrant of France and A Bargain of Necessity from The Reign of Terror/The French Revolution are missing.
23-episode run of surviving episodes between Prisoners of Conciergerie (The Reign of Terror/The French Revolution) and The Lion (The Crusade/The Lionheart/The Crusaders).
Alternating between lost-surviving-lost, we have The Knight of Jaffa, The Wheel of Fortune and The Warlords from The Crusade/The Lionheart/The Crusaders.
14-episode run of surviving episodes from The Space Museum (The Space Museum) to Checkmate (The Time Meddler) and thus for the rest of Season Two.
10-episode run of lost episodes at the start of Season Three running from Four Hundred Dawns (Galaxy Four) to The Nightmare Begins (The Daleks' Master Plan). Yes, I'm counting Four Hundred Dawns as missing. Even though there's an 8-minute piece of footage in it, that doesn't mean it's complete.
Alternating between surviving-missing-surviving, we have most of the rest of The Daleks' Master Plan: Day of Armageddon, Devil's Planet to The Traitors, Counter Plot, Coronas of the Sun to Golden Death and Escape Switch.
6-episode run of lost episodes from The Abandoned Planet (The Daleks' Master Plan) to Bell of Doom (The Massacre of St Bartholomew's Eve/The Massacre).
4-episode run of surviving episodes through The Ark.
3-episode run of lost episodes through The Celestial Toymaker from The Celestial Toyroom to The Dancing Floor.
5-episode run of surviving episodes from The Final Test (The Celestial Toymaker) to the last episode with its own title, The OK Corral (The Gunfighters).
4-episode run of missing episodes through The Savages.
4-episode run of surviving episodes at the end of Season Three through The War Machines.
4-episode run of missing episodes at the start of Season Four through The Smugglers.
3-episode run of surviving episodes through The Tenth Planet from episodes 1-3.
13-episode run of missing episodes through the Doctor boundary from The Tenth Planet #4 to The Underwater Menace #2.
After episode 3 of The Underwater Menace (which survives), we have a 2-episode run of missing episodes from The Underwater Menace #4 to The Moonbase #1.
Alternating between surviving-lost-surviving, we have the rest of the Moonbase.
4-episode run of missing episodes through The Macra Terror.
Alternating between surviving-missing-surviving, we have the first three episodes of The Faceless Ones.
4-episode run of missing episodes from The Faceless Ones #4 to The Evil of the Daleks #1.
After the surviving second episode of The Evil of the Daleks, we have a 5-episode run of missing episodes through the rest of The Evil of the Daleks.
4-episode run of surviving episodes through The Tomb of the Cybermen.
After the missing first and surviving second episodes of The Abominable Snowmen, we have a 4-episode run of missing episodes through the rest of The Abominable Snowmen.
After the surviving first and the lost second and third episodes of The Ice Warriors, we have a 3-episode run of surviving episodes through the rest of The Ice Warriors.
After the missing first and second and the surviving third episodes of The Enemy of the World, we have a 3-episode run of missing episodes through the rest of The Enemy of the World.
After the surviving first episode of The Web of Fear, we have a 13-episode run of missing episodes from The Web of Fear #2 to The Wheel in Space #2.
After the surviving third and missing fourth and fifth episodes of The Wheel in Space, we have an 11-episode run of original versions of episodes that survive from The Wheel in Space #6 to The Mind Robber #5.
The original versions of The Invasion #1 and #4 are missing, but they have been animated for DVD. So if you want originals, you'll have a 2-episode run of survivors between them and a 14-episode run of survivors after them from The Invasion #5 to The Seeds of Death #6. But if you don't care about originality and absolutely insist on counting The Invasion #1 and #4, we've got a 27-episode run of survivors from The Wheel in Space #6 to The Seeds of Death #6.
After the missing first and surviving second episodes of The Space Pirates, we have a 3-episode run of missing episodes for the rest of The Space Pirates. After that, everything survives. Except...
List of black and white-only episodes from the Pertwee era
Yeah, there are some Pertwee episodes that are only available in black and white. So if you count the colour versions of those as missing, we've got a longer list!
22-episode run of surviving episodes over the Doctor boundary from The War Games #1 to The Ambassadors of Death #1.
3-episode run of black and white episodes through The Ambassadors of Death from episodes 2 to 4.
After the coloured The Ambassadors of Death #5 and 6 and the black and white The Ambassadors of Death #7, we have an 11-episode run of colour episodes from Inferno #1 to Terror of the Autons #4.
6-episode run of black and white episodes through The Mind of Evil.
We have a 61-episode run through Seasons 8-11 from The Claws of Axos #1 to The Time Warrior #4.
After Invasion of the Dinosaurs #1, everything is available in colour - except 60% of the 6-episode Shada, which has no complete episodes but might just appear on DVD - probably the same way as it did when it appeared on VHS in 1992 with Tom Baker narrating the bits that weren't filmed.
Phew - that took so long I had to save it as a draft halfway through! Combine the facts that it's such a long list and I am going to bed after possibly wrapping a few Christmas presents and e-mailing this to my dad for him to put in his blog, I can't just read it all through in one go and I don't feel like doing that right now, but you can mention spelling mistakes (I do not spell colour wrong. That's how you spell it in the English that I speak - aka English English) and things I did extremely weirdly in the comments.
He is his father's son, obviously!