After the Opponents Overcall

What happens after partner opens the bidding and the opponents overcall?

Let's start on the 1-level.

The opponents overcall partner's 1-level opening bid with a suit bid.

If partner opens 1-of-a-suit and the opponents overcall in a suit:

&New suits by responder are forcing one round (if on the 2-level, 10+ points).

Example: 1 (1) 1 = forcing one round (+ points)

1 (1) 2 = forcing one round and 10+ points

&New suits by responder promise 5 or more cards, except when the opponents overcall 1 with 1 and we respond 1 or 1.

Example: 1 (1) 1 MAJ = 4+ in that major
1 (1) 1 = 5 or more spades and 1 (1) 2 = 5 or more clubs.

&New suits by responder on the 3-level (not a jump, though) are GF. Example: 1 (2) 3 = 5+, GF

&New suit jumps by responder require partnership agreement (fit-showing is possible, but most players would likely play this as a weak jump in competition). Example: 1 (1) 3

&Single raises are natural and mean what they would have meant without the interference. If forced to raise to the 3-level, it shows a little extra. Example: 1 (2) 3 = 3+ and 8-10 in support (approximate)

&Cue-bidding the opponent's suit shows a limit-raise or better. Example: 1 (2) 3

&Jump raises are preemptive (assuming modern style). Example: 1 (2) 3

&Notrump bids are natural (1NT=6-10, 2NT=11-12, 3NT=13-15) with a stopper in their suit (and balanced).
Example: 1 (1) 1NT=6-10 with spades stopped

More examples:

OPENER	Opponent	RESPONDER	MEANING
1	1	1 MAJ	4+ cards 6+ points
1	1	1	5+spades, 6+ points
1	1	2	5+ 10+points
1	2	3	5+ GF
1	1	2	Partnership agreement
1	1	2	4+, Limit Raise+
1	1	2NT	11-12 balanced NF, stopper
1	1	3NT	13-15 balanced, stopper
1	2	3	4, weakish (0-7)
1	2	3	3+, Inv+

Doubles are negative. You can read more about negative doubles here.

The opponents overcall with 1NT:

If they overcall 1NT, assuming no conventions, a double is penalty, and a new suit bid is natural, NF

Examples:

West	North	East	MEANING
1	1NT	Double	Penalty
1	1NT	3	Preemptive
1	1NT	2	6+, NF

The opponents overcall with a Conventional bid to show a 2-suited hand Michaels Cue-bid:

Details on this topic are covered here.

The opponents overcall with preempt:

A new suit by responder is forcing for one round on the 2-level. If responder bids a new suit on the 3-level, it is game forcing.

The opponents overcall our preempts:

Doubles are penalty. Raises are competitive/further preempting--not inviting.

For example:

West	North	East	MEANING
2	2	Double	PENALTY
2	3	3	NOT INVITING 4

updated: Dec, 2020