Smolen is a convention used by a responder to a notrump opening bid (or natural notrump overcall).

 
It is used when the responder is 5-4 in the majors (either way).

It is used only when the responder has enough strength for game.

Here is an example hand for responder to 1NT:

AJ542
KJ87
2
J103
.

After partner's 1NT, start with Stayman.  (Transferring to spades and then bidding hearts should promise at least 5-5).

If the 1NT opener shows a 4-card major, this hand is easy (just raise to game in that major).

But, what if opener answers with 2, denying a major?

Now, the contract of 4 is out of the picture (no 4-4 fit), but 4 is still a possibility (there could be a 5-3 fit). So, responder has to indicate that he has 5 spades.

He is too strong to bid 2; he must force to game. So, in Standard bidding, he would jump to 3. This announces 5 spades and GF values. By inference it shows 4 hearts (otherwise, he would have started with a plain transfer to spades and not used Stayman). So, in Standard Bidding, 1NT-2-2-3-of-Major shows 5 in that major, 4 in the other major and enough for game. Opener will then choose between 3NT, or playing in responder's 5-card major.

The Smolen convention makes a slight improvement on this auction. Responder, instead of jumping from 2 into his five-card major, jumps into his four-card major! Why? Because now, if opener wants to play in the five-card major, it is played from his (the strong) side.  As is usually the case after a notrump opening, you want the strong hand playing the contract (for opening lead purposes). So, using Smolen, 1NT-2-2-3-of-a-Major shows 5 cards in the other major, and by inference, four cards in the major jumped into.

Smolen after 2NTSmolen is also used after 2NT-3-3. Responder bids the major in which he has 4 cards, thereby showing 5 in the other major and potentially right-siding the contract.

Of course, Smolen also applies after our side makes a natural strong notrump overcall (systems on).

_{Last update: June 2012}