As Peter Clark has said this is the million dollar question in bridge bidding! Bids can be classified as forcing or non-forcing, but that is not the whole story. A forcing bid can be forcing for one round of bidding or forcing to game/slam. A non forcing bid can be also invitational, but still non forcing. A forcing bid demands a further bid by responder, whereas a non forcing does not. Any bid that describes the hand within well defined limits, both shape and points, is non forcing.

A change of suit response to opener’s suit bid should always be regarded as FORCING, even if responder has already passed, with one exception. Without this, responder is forced to make jump bids, so reducing the bidding space to develop the auction. If opener limits the hand by re-bidding the suit at the two level, then a new suit by responder is forcing to game

The exception is: Opener has minimum hand and 3 cards in responder’s suit and responder has already passed.

So what responses to an opening bid in a suit are non forcing? Well responses in no-trumps (non conventionally), raises in opener’s suit(support), game bids in a new suit.

Re-bids by either player in no-trumps or suits are non forcing. Jump re-bids by opener in a suit are non forcing if the first response is at the 1 level, but forcing if the response is at the 2 level.(which shows 10+pts). A jump re-bid by opener should be a 6 card suit and 16pts, but a jump re-bid by responder may show a 5 card suit and around 13 pts, and is forcing.

A simple rebid by opener is forcing for 1 round, if the response by partner is made at the two level, forcing to 2 of openers first bid suit (many players play this as forcing to 2NT).. On the other hand, a simple rebid by opener at the 2 level when partner's first response is at the 1 level can be passed (responder showing preference to opener's second suit)

1......1, 2 can be passed

1......2, 2 is forcing to 2

After opener or responder has limited the value of the hand, any new bids by that player must be non forcing For example responder has made a response of 1 no-trumps, so any new suit by responder is non forcing. Responder may be forced to bid 1NT, not having enough points to bid at the 2 level, but holding a long suit.(1….1NT; 2 ….2 . Responder has a 6-9 pts with a 6 card diamond suit)

Which opening bids should be regard as forcing for at least 1 round? Any conventional bid is forcing if it does not describe the suit bid. This includes any “Strong Club” system opening of 1 . Any strong two bid that is alerted (e.g.2 in Acol). An opening two bid in a natural suit should be announced however as "forcing " or "non forcing", Many players play this opening bid as forcing per se but it is a matter of style.

Opening bids described as “weak”, e.g. weak twos, or threes, and opening bids at the game level, i.e. 4 are non forcing. Agree with partner what a change of suit means if partner opens a weak two in a major suit, since many players play a simple change of suit is just looking for a better contract. Changes of suit to a weak three opening are normally played as forcing. Of course opening bids in no-trumps are non forcing. If 1NT is doubled, any bid by responder at the 2 level is natural and non forcing.

Conventional responses to a limit bid opening of 1NT or 2NT are forcing for 1 round, with Stayman and transfers being the best known examples, but once the opener has replied to a tranmsfer, that bid is non forcing. Bidding a second suit after a transfer is completed is forcing to game (e.g. 1NT….2 ,…2 , 3 ). Note that had the last bid been 3 that is non forcing but invitational. Suit responses at the 3 level to a 1NT opening are forcing to game ( e.g. 1NT……3, asking opener to bid 3NT or 4)

One area for partnership discussion is after partner has opened 1NT (12-14), and opponents overcall in a suit. Bids by partner are normally played as non forcing at the two level. A bid at the 3 level is competitive but encouraging and the opener should consider bidding 3NT if he holds two stops in the suit bid by the opposition and semi support for partner's suit. The bid at the 3 level is however non-forcing, whereas a new suit at the 3 level is normally foring to game, but opener has limited his hand

Conventions such as: 4^th suit forcing, directional asking bids, and long suit trial bids are forcing for 1 round. Cue bids of the opponents suit are forcing, so are cue bids when only your side are doing the bidding. Any new suit at the 3 level by opener should be forcing, i.e. a high level reverse. Blackwood and Gerber are forcing. So are overcall conventions such as Michael’s Cue bid or CRO.

Doubles for take-out at all levels are forcing. A double of a conventional bid is usually lead directing so is non forcing. After partner has doubled 1NT, any further double by your side should be for penalties.

When either player has bid 2 suits, the second suit bid can be passed, but preference should be given to the first suit with equal length or better. Bids that are non forcing but invitational include raises in suits or no-trumps. Examples are 1NT….2NT; 1….3; 1….2…3, the last bid being an invitation to game but can be passed

Overcalls of opponent’s suit bid, even jump overcalls, are non forcing. Overcalling a suit bid with 1NT (15-17pts) is non forcing. If you want to force, double first, then either bid a new suit or bid no-trumps.

After opener has opened at the 2 level with the strongest bid in your system, and then bids a suit, that bid is absolutely forcing to game

Can you pass a forcing bid? Yes if opponents intervene with a bid, otherwise no.