Preemptive Opening Bids in Bridge
After our side opens with a preempt we must have some solid partnership agreements about what happens next.
An opening bid at the 3 level is a preempt showing a 7 card suit and a weak hand. It can also be a 6 card suit if the vulnerablity and table position are appropriate. Preempts take away bidding space from our opponents. They're also reasonably descriptive of our own hand so partner will have some idea of if and how to respond.
3 level opening bid
Here's a pretty normal preempt.
South has a good 7-card suit and less than an opening hand. Even if you don't make your contract you'll hopefully come close enough to make it a good sacrifice.
Preempts take up our side's bidding space as well as our opponents'. If you have a good major suit as a side suit you might choose not to preempt.
If you open 3♦ you'll make it harder for your side to find a potential spade fit.
Preempting with a 6 card suit
If you're playing weak 2 bids you might open 2♥ with the following hand.
Many players would also open 3♥, especially not vulnerable.
Responding to a preempt
Change of suit
The first thing to discuss with your partner is whether a change of suit is forcing. After that, how should opener rebid?
3NT says no fit with responder, that's all. Don't go past 3NT!
This time opener has a fit with responder.
Jxx is enough to support spades.
If opener bids a new suit it shows trump support and first or second round control in the suit.
4♣ by the opener shows spade support and either the Ace, King, a void or singleton in clubs.
See also key card over a preempt
Here's a hand where the opposition make a preempt.