This convention was first invented by my good friend, Marty Bergen, when we were bridge partners in the 1980's.
As first written and played, here were the responses to a 1-of-a-Major opening:
3=6-10 in support and 4-card support
3=11-12 in support (limit raise) and 4-card support
3-of-the-major (raise)=0-5 and 4-card support
There are many add-ons and revisions, some as follows:
Inversion revision (make sure you and your partner know if you are playing the original way or this way):
The 3 and 3 responses are reversed in meaning
A jump to 3-of-the other major has a special meaning (there are many ways out there--I suggest not bidding it)
3NT=13-15 balanced with 4-3-3-3 (I recommend this)
4-level=Many possibilities (In "Standard" it would just be a Splinter Bid).
PH and Competition
It is crucial to have agreements regarding if this convention is used by a Passed Hand (I recommend not) or after a double or overcall (I recommend not). Some variations use the convention in all of these situations.
Because of all the potential confusion (all 3 of the sections above), I don't recommend this convention (sorry, Marty). I actually like a jump to 3-of-a-lower suit to be natural and invitation. So, 1-3 shows something like: 2
. You must decide with your partner if you are playing Bergen Raises, how you are playing them, or a possible alternative.