This is your premium source if you want to write the very first thesis about the history of domino-toppling... :D
The idea to set up dominoes in a line and then topple them is probably as old as dominoes themselves, and they are pretty old. The comparison that something looked like a line of dominoes falling down can be found in newspapers from the 1930's already.
Nevertheless, domino-toppling as a serious pastime didn't form gradually, but very abruptly - it was started solely by Bob Speca in 1972. Domino Day, this homepage and everything else related to the topic is exclusively his fault ;-) Or rather the fault of his science teacher, Mr Dobransky.
Speca was a 15-year-old student at Mapleton High School, Pennsylvania, when his interest in dominoes was triggered all of a sudden: Mr Dobransky explained the mathematical theory of induction by comparing it to a line of dominoes that would never stop toppling if it was endless; and Speca, who had only heard of the idea of setting up dominoes when President Eisenhower had coined the name "domino theory" for some countries in Asia triggering each other into communism, was rather interested in what such a domino line would look like than in mathematics. (I wonder why he didn't care about that when he heard of the "domino theory"... is communism that much more interesting than domino-toppling? :D)
He went to a local store the same afternoon, bought 112 dominoes, set them up on the table at home, toppled them, and was fascinated.
So he just went on with it. His collection of dominoes grew bigger and bigger, and soon he would start doing patterns instead of just lines and do larger setups in the basement. He invited friends to watch the falldown; they were thrilled, and soon he was in the newspapers.
He wasn't aware that he was the first domino-builder in the world though - when one of his friends wondered if his setups were the largest in the world, he was surprised to find no such record in the Guinness Book. So he created that record.
Since he liked repdigits, his first inofficial records had included 5,555 respectively 8,888 dominoes; and now the first world record had 11,111. There are contradiciting sources on the date of the event: recordholders.org states it happened in December 1974, Speca himself said "in 1975" in an interview, and so did a press statement announcing a project he did in 2011 with the same number of dominoes. What I can say for sure is that it happened some day between November 1974 (because on November 1st, 1974, a newspaper article about him stated that he was planning to set an official record) and March 1975 (because after the record, he was invited to the Tonight Show for "sometime that spring", which wouldn't make sense written in April).
Wait, the Tonight Show? Yes, just shortly after his first serious achievement as a domino-builder, a childhood dream of Speca came true when he received a positive answer to a letter he wrote to the show asking if they would be interested in featuring him. He presented a setup of 7,000 dominoes there, and the audience was thrilled.
His appearance used to be available on YouTube, but was removed due to a copyright claim by the producing company. I still have it because I downloaded it before, but of course can't put it at disposal here.
That broadcast, of course, was the starting shot for a competition about the world records. Just a while after Speca's performance on the show, a couple of students broke his record, toppling 13,382.
And from that on, a competition for the world record started - partly thanks to a charity organisation called National Hemophilia Foundation. Someone there called Tom Harrington realized what potential domino-toppling events, especially record-breaking ones, would have as a fundraising method. By having each domino (or perhaps a box of 100 dominoes) sponsored with 1$ or something, you could raise nice amounts for charity. And that idea actually worked because a world record gets a lot of attention in the media, of course.
Within a decade after Speca's 11,111 dominoes, the world record was broken 12 times, and most of these events were organised by the NHF. Speca gained the record back several times; the other record holders were the forementioned Seattle students, Michael Cairney from Scotland, a duo formed by Erez Klein and John Wickham from Iowa respectively South Carolina, Alistair Howden from New Zealand, and finally Klaus Friedrich from Germany. (And Jerry Clerc and a bunch of volunteers who broke the record in 1982 - but apparently it wasn't official, because the next official record included less dominoes.) Other notable builders who already started in those very early days of domino-toppling were Scott Suko and Dan Beckerleg, who among others participated in a unique around-the-world topple (using satellite connections to continue the chain reaction on the next continent) with 300,000 dominoes in 1986. In 2000, Suco made a domino-toppling tutorial which is available here.
Friedrich's record of 281,581 dominoes in 1984 was sort of the end of an era - he was the last person to set the record single-handedly (in that category, it even remained the record for almost two full decades!), because two years later, a new era began.
(That is, a new era for domino fans :-D Which were VERY few people back then.)
The whole thing was started by the Dutch airline KLM. In order to attract Japanese people to come to the Netherlands, they wanted to show videos of domino-toppling world records during their flights. (What a weird idea! But apparently they had found out there was already a bit of a domino craze in Japan. Cudos to KLM :D) A group of 45 students of the Delft University finally agreed to produce a video for them - including their own event where they would break the world record.
One of these students was 21-year-old Robin Paul Weijers. He was a creative young man, but had obviously totally ignored that fact when chosing his program of study: technical engineering. So, domino-toppling on the one hand, and this young, enthusiastic, creative student on the other hand - it was love at first sight ;-)
Although the event the students finally organised didn't work perfectly at all (Weijers called it "embarrassing" later), they had broken the world record by far, and Weijers had really gotten into the spirit - two years later, he was the main organisator of the second edition of these "pre-Domino-Days".
What followed was a break of ten years. Strangely enough, no source gives any explanation or reason for that. (If I ever meet Robin Weijers in person, that's probably going to be the first thing I'll ask him.) Propably he just finished his studies, he does hold a degree in technical engineering today, and in marketing as well.
Anyway, with his third world record attempt in 1998, he started the series of actual "Domino Days" (the events in 1986 and 1988 are not counted as official Domino Days), first calling it D-Day until someone noticed the other meaning of that expression.
It can't be overestimated how much attention domino-toppling received through that. Without Domino Day, it would most likely still be a hobby only very few had even heard of yet. Nearly all domino-builders I know - and I know many - were brought to it by Domino Day, and the very few others were triggered by one of those other builders. In other words: Without Domino Day, domino-toppling would still have about as many fans as the national handball team of the Faroe Islands.
Domino Day has reached up to 85 million live viewers all over the European Union, including up to 14 million in Germany (about 17% of the total population - imagine 50 million viewers in the United States!), and now, after eleven editions, I hardly ever have to explain to anyone what I mean by "domino-building" when I present myself to someone - the common answer is "Oh, like at Domino Day?"
The downside is that many viewers suppose that RTL, the channel that has been broadcasting the event in Germany since 1998, "invented" Domino Day, and domino-toppling in general, as a new show concept, just like they come up with new soaps, Reality TV and quiz shows. Since about 2006, the popularity of Domino Day has shrunk in Germany, and I have often read comments like "Why is RTL doing a new edition every year, this thing has gotten out of fashion".
However, Domino Day has made thousands of people, mostly kids, try domino-toppling on their own, especially in the Netherlands and Germany.
Most of them really didn't go any further than trying. Many do go on for a while, but then lose interest after a few weeks, and that repeats every year when a new Domino Day is broadcast. (I've always been surprised how many random people I've met reacted to my domino-toppling enthusiasm with "Oh, I did that for a while, too. I still have a box of 300 pieces at home.") Some seem to be really dedicated to it, set up dominoes in every minute of free time they have, create some really great setups - and then, after a year or so, they slowly become less active, concentrate more on other pastimes, until they realize that they're not really interested in domino anymore. I've mourned (don't take me seriously there) many talented domino-builders on YouTube who have become inactive like that. Every few months, they post a video saying "I'M BACK!!!!", and then they are gone again...
And then there are the very few, just a few dozens of "dominoists" who are really, REALLY dedicated to it and don't even think of thinking of quitting that hobby. Well, that might be exaggerated. In August 2006, I had something like a "burnout" - I was depressed because it looked like I had basically discovered anything spectacular you can do with dominoes. It sounds weird, but I was really desperate. Two weeks later, I came to think of an awesome new effect, and I was back in the spirit...
Domino-toppling is still such an unexplored hobby that everyone who starts now (and even more so, anyone who has started years ago), is a bit creative and really puts dedication into it is a pioneer.
And nobody, besides Robin Weijers, deserves being called a domino pioneer more than FlippyCat. If you've never heard that name before: 1.) Shame on you. 2.) Good that you're hearing of him now. 3.) Here we go: FlippyCat was the very first domino-builder to post his videos on YouTube. By now, hey have been watched more than 100,000,000 (yes, that's a hundred million) times in total, and FlippyCat is widely considered to be the best domino-builder in the world apart from Domino Day.
I'm refering to him as FlippyCat simply because he doesn't want his real name to be published. He prefers to stay anonymous and doesn't show his face in his videos either. His real name, age and even an "uncensored" photo have found their way into the internet though... but since no one except for me seems to have found them so far and because I want to respect Flippy's wish to stay anonymous, I won't name them here. Feel free to search them, but rest assured you most likely won't find them on Google.
His trademark used to be his cat, called Flippy of course, who would appear in most of videos, sometimes even toppling the first domino. Sadly, he had to be put to sleep on July 6th, 2010.
Anyway, FlippyCat had started what has become a great community of domino-builders on YouTube today. He founded a group (back at the time when YouTube groups still made sense) where they would discuss anything domino-related, announce new projects, share tricks (and gossip about each other...) and so on.
I have made a compilation video that shows the most spectacular clips out of the thousands of domino videos on YouTube. 78 domino-builders' creations are included (all of them gave me written permission to use their videos).
YouTube is the place where domino-builders come together - there are no assosiactions, unions etc. yet, and websites like dominofans.com don't really have a notable lot of traffic either. The interaction happens on YouTube, and maybe in regular chats such as icq.
One reason for that is that most domino-builders are still teens or kids. Remember, practically everyone started as a kid after watching one of the Domino Days - it's still a very, very new hobby, we're the first generation of domino fans. With my 18 years of age and 11 years of experience, I'm almost something like a veteran...
So, an official organisation doesn't exist yet simply because it's all still too unformed. However, many domino-builders have passed their hobby on to their friends at school, and - bingo, we have a domino group. Especially in Germany, there have been many small domino events (= 3,000 - 20,000 dominoes) in many schools, gyms, town halls etc. Local newspapers write a small article about them, 20 people come to watch the falldown, and that's it, usually. I have been part of such a group, too, from 2002 to 2005 - we've had eleven "Domino Days", which is already record-breakingly many.
Some similair groups also exist in the Netherlands, the United States, Hungary, Spain and probably a few other countries. I suppose there are many I have just never heard of.
Like I said, most of these groups come apart soon again. A few have become a big deal though: A group from Türkheim, Bavaria currently holds the German domino record with more than 440,000 dominoes (they had sponsors); they currently don't plan on new events though. Individual Domino Toppling (IDT) was the first group that brought together domino-builders through YouTube, mostly from the Netherlands - but they have also quit. Now the most remarkable group is by far the Cologne Domino Team (CDT) that unites the best of YouTube's German domino-builders - something like a very loose first shape of a German nation team ;-) I'm a member of CDT; you can read more about us here.