Main game

Two teams of three competed in each game. A team consisted of one contestant and two celebrity guests. The teams were shown the beginning and ending words of an eight-word chain. Each word is related to the word above it and below it, the connection could be either a word association or a phrase. A sample chain could be:

TWIST
ANKLE
BRACELET
CHAIN
GANG
WAR
STRATEGY
CHESS

The challenging team began the game. In the event two new players were competing, a coin toss determined which team went first. Usually, the challengers were the blue team and the champions were the gold team.

As the game continued, the words would be revealed one letter at a time. A player's turn consisted of calling for a letter in the next word above or below one of the already revealed words and then guessing the word (note that the last letter of each word is not revealed). A correct response won one point for each letter in the word (two if the word had a '+' mark next to it) and that team kept control of the board. If the player in control was incorrect or gave no guess, control went back to the other team. The game continued until either one team scored 50 points, or the chain was finished. If that happened, another chain was put up and the game continued until one team reached the goal of 50 points, any letters exceeding 50 points are not included in the player's score. That team's contestant won the game, $250 (later dropped when the final version of the endgame was introduced) and the right to play for $10,000 in the bonus round. The losing player received $5 a point for playing (changed to parting gifts with the third endgame).

Instant Reaction

In the bonus round, the two celebrities from the winning team attempted to get the contestant to guess a series of words or phrases by constructing a question one word at a time. The celebrities alternated giving words to construct the question, then hit a bell signaling the contestant to respond. Cash was awarded to the contestant for every correct response.

In the first format (which only lasted the first week of the series), the team was staked with $1 and had a 60-second time limit. Each correct response added one half of a zero behind the $1, meaning that after two correct responses the player would win $10, after four the player would win $100, and so on up to the $10,000 maximum.

For the next four weeks, the time limit was increased to 90 seconds, and the first correct response was worth $1, with the next three each adding a zero behind it. At that point, the contestant's winnings would be $1,000 and the next four correct responses each added $1,000 to their total. The ninth overall correct response augmented their total to $10,000.

The third format had the same time limit, but each of the first nine correct responses was now worth $100, and the tenth correct response increased the contestant's winnings to $10,000. After two weeks, the format was slightly modified so that the contestant was staked with $100 at the start of the round, thus reducing the number of correct answers needed for a $10,000 win to nine.

If at any point a contestant provided an incorrect response, a celebrity gave two words in succession, accidentally gave part of the answer, or passed the word, the word was thrown out and gameplay continued to the next word.

Champions remained on the show until they were defeated or until they won ten matches.

Stewart later developed and expanded the bonus round of Chain Reaction into the game show Go.

"Instant Reaction" would later be revived as the bonus round on the first Dylan Lane-hosted version of Chain Reaction.

Main game

Each chain comprised seven words. The teams were reduced to two civilian players each and each was given one responsibility. One teammate was the letter giver and decided whether to give a letter to his or her partner or the other team's word guesser. As before, a correct response was worth points and control of the board. In round one, each word guessed was worth 10 points, but the final word guessed in that chain was worth 20 (changed to 15 in season two). In round two, these values escalated to 20 points each and 40 points for the final word. If a fourth chain was needed to decide the game, the point values were 40 points per word and 80 for the final word. The first team to score 200 points won the game. That team played the bonus game and returned to the next show.

During the run, two methods of earning bonus money were used. In the first season, the middle word of the second chain was also a bonus word (designated first by an asterisk, then by a dollar sign) worth $250 for the team that guessed it. For seasons two to four, the players played a Missing Link. The team in the lead would be shown the first and last words of a three-word chain. If they could guess the word in between with no letters revealed, the team received $500. Every wrong guess added a letter while taking away $100 from the potential payoff.

For seasons three and four, only solo players participated and a score of 300 won the game. The players now had to decide whether to take a letter for themselves or give one to their opponent.

Champions remained on the show until they were defeated or held their title for five consecutive days. During the first season, any team that retired undefeated received a $5,000 bonus.

Bonus chain

The winning team/player could collect a cash jackpot by completing one last word chain. The team/player was shown the first word in a chain and the initial letter of the other words. One at a time, the player(s) would guess at the next word in the chain. For each wrong guess, the next letter would be filled in and a letter deducted from their account. If the team could finish the chain before running out of letters the team won the cash jackpot. If not, they (or he/she) won $100 per word, including the one at the top. The jackpot began at $3,000 ($2,000 with the solo players) and $1,000 was added each day it was not claimed. The highest pot was $16,000. While Emmons was host the account was nine letters. When Geoff Edwards took over it was lowered to seven. During season one, if there was extra time afterward, another bonus round was played, this time worth $1,000 for the team's favorite charity.

The bonus chain was removed in season five because the end of season four had an elimination tournament of champions, where the sixteen top winners of seasons three and four returned in a tournament format (sixteen players reduced to eight, then down to four and then down to two). The final winner of the final game won $20,000 and the runner-up won $2,000. Games were all played to 500 points.

The $40,000 Chain Reaction

On New Year's Eve 1990, the show was revamped with a tournament format featuring 128 players competing for $40,000. The game was played as before, but there was no bonus chain and two new players competed in each show. The values for each chain remained the same, but if a fifth chain was needed, the point values were 50 points per word and 100 for the final word. In the event of a game ending with only four chains played, co-host Charlebois would play the fifth chain against the day's winner.

Eight players competed on the first four shows. After four days, those four winners played two each for the next two days. Those two winners played on the seventh day and the winner of that game won $7,500.

The player who led after the second chain got to play a Missing Link for $300. The Missing Link changed its format as well. After the change, the first letter of the middle word was given, the first letter was worth $300 and subsequent letters reduced the value by $100.

After sixteen $7,500 tournaments were played, those 16 players played in a single-elimination tournament. The semi-finals were double-elimination and the two players remaining played one game for $40,000.

Home game

Each day, before closing the show, Charlebois would present the answer to yesterday's home game and the current game. The home game consisted of a Missing Link (see above) and was actually referred to as such during the first season, but later renamed simply "the home game" when this format was adapted as the new round two mini-bonus in the second season. The home game first started while Emmons was still hosting, during which time he presented the home game alone and encouraged viewers to write the chains down on a piece of paper. Charlebois didn't start coming onto the stage to present the home game until Edwards took over the hosting duties, per the aforementioned Cancon regulations.

Main game

There are four chains in the main game (not counting the Speed Chains). The gameplay is similar to the NBC and USA/Global versions, except that the words in the chain are now always two-word phrases or compound words. In the first season of the 2006-2007 version, the final letter of a word would be revealed (though the fact that it was the final letter was not announced, and sometimes was not evident). At that point, if the team did not guess the word correctly, the word was revealed and neither team received the money. Since the second season of the 2006-2007 version, the last letter is not revealed (as in the 1980 and 1986-1991 versions), although a shuffling placeholder (or a blank space in Catherwood's version) is shown in place of the last letter. If the word was not correctly guessed, the other team had a chance to either guess that word or choose a different space but did not receive another letter.

In round one, each correct word is worth $100, round two words are worth $200 and words in round three are worth $300. Whichever team was behind going into a round started the next round (in the event of a tie, the team who did not start the last chain started the next chain). In the first two GSN runs, all chains that were not Speed Chains were seven-word chains. In the 2021 version, the first three rounds are each played with a six-word chain.

In the fourth round, each team is required to wager between $100 and $500 of their bank before being given their letter. If correct, they win their bet and keep control, if not, the amount of the bet is deducted and they lose control (or lose the game if they wagered the entire bankroll). In the 2021 version, the fourth round is the only round played with a seven-word chain, with wagers between $100 and $500, except a team can now wager up to $1,000 once there is only one word left to be revealed in the chain.

A team can win the game if either they are ahead after the fourth round, or if at any time the other team's bankroll is reduced to zero. In the event of a tie at the end of the fourth round, the Tiebreaker is played.

Tiebreaker

In the 2006 and 2015 versions, if the fourth round ended in a tie, the teams were given alternating Speed Chains in a "sudden death" format. If one team did not solve their Speed Chain, the other team need only solve their next Speed Chain to win the game. Both teams kept their money, and the losing team received unacknowledged parting gifts as well.

In the 2021 version, the Tiebreaker uses only one Speed Chain. The team that went first in the fourth round has the option to play the Speed Chain or pass it to the other team. The tiebreaking Speed Chain is played in the same manner as after each of the first three rounds of regulation play (including the seven-second conference). If the team playing the Speed Chain successfully solves the chain, that team wins the game. If not, the other team automatically wins.

Bonus Round

The winning team then advances to the bonus round, which was different for each version.