DSIP rule summary

1. Unless explicitly rendered otherwise by one of the events listed below, all doubles are either pure takeout or cooperative, that is to say that you expect partner to take the double out, but you won't be unhappy if he doesn't; level is immaterial – even if the last call by the opponents is 7♥.
2. If either partner on our side does one of the following, doubles become penalty:
1. bids notrump "to play" (generally this is at the 2-level or above or at the one level when showing a stopper);
2. makes a penalty double (e.g. a lead-directing double of an artificial or cue bid) or passes partner's double, or makes the third double for our side;
3. redoubles (of any sort);
4. shows a two-suited hand (except that if one of the suits is unknown, it's best to play partner's first subsequent double as asking which is the suit);
5. makes a cuebid or bids the last remaining unbid suit (or bids the "fourth" suit as a force);
6. jumps the bidding (this last item covers the gamut of preemptive bids and fit-showing bids -- because they tell partner so much information in one bid, he/she is now in a much better position to make a penalty double -- note however that a subsequent double by jumper is not typically 100% penalty).
3. If we pass over a suit bid on our right in a competitive auction and subsequently double that same suit, thus exposing the pass as a trap;
4. If their side does any of the first four of the above actions (they can jump all they want, it's only when we jump that penalty doubles are turned on).

For more background and discussion please see my earlier post: Double!

Postscript:

The above was published April 9th 2010. It's now Oct 18th 2014 and much water has flowed under the bridge. The triggers (rules) mentioned above have not changed significantly since then, but there have been revisions. It is probably time to write up a new summary, especially rule 3 which essentially [should] cover[s] all of the exceptions. If you would like to read all of the relevant posts on this general subject, then follow this link: all DSIP posts.