Wilkosz 2D

2D opening, showing 5-5 distribution, too weak to open at the 1-level (usually 6-7 losers and 6-10 HCP.)
It can be ANY two suits except for both minors - 5 possible combinations.
The three most common responses are 2H, 2S, and 2NT:
2H - Opener passes if he has hearts, bids 2S if not.
2S - Opener passes if he has spades, bids 3 of his minor if not.
2NT - Asks opener which 2 suits he has:
he rebids       
3C - clubs + major       
3D - red suits       
3H - majors       
3S - spades + diamonds
There are other responses (mostly to show hands where responder can support any of 2 or 3 suits and is guaranteed a fit) and rebids (for opener to show 6-5 or more extreme shape) but these are rare, and not every pair will play them the same.
If 2D opening is doubled, responder passes if willing to play diamonds, redoubles to force opener to name his major.

Suggested defense

If your side has values for game, tend to play 3NT in preference to 4M when you can, because of the elevated risk of adverse ruffs and/or bad trump breaks.
Over 2D:
Pass: any hand with nothing to say, and any hand that's a classic takeout double of diamonds (3-suited or semibalanced, with short/weak diamonds) even if fairly strong.
Double: balanced or semibalanced ~13-16 (or 20+), with at least Hx or xxx in diamonds
2M: Sound 2-level overcall values
2NT: Balanced 17-19.
3m: Sound overcall values, usually 6-card suit.Jump shift: natural and strong.
Over 2D-P-2M:
Double - takeout (partner will often convert); other bids natural, including 2NT
Over 2D-X-Pass:
Pass: Willing to defend 2DX if opener has 5 diamonds and passes. Do not pass with a minimum and short diamonds!
2M,2NT,3C: Natural, nonforcing.
3D: Pick a major
3M: Natural, forcing

More information and credits:For details about the opening side's other bids, see Greg Matula, The Polish Club, chapter VI. The suggested defense here is patterned after David Burn's defense used by the English international team. Other defenses exist, especially in regard to the meaning of 2NT and the decision whether to double or pass in direct deal. One common variation (for the stout of heart!) is to play 2D-P-2M-X as either takeout or penalty, partner guesses which based on his own hand.