Opening Bid:   One Diamond - 11-16 HCP

This particular bid is probably the most frequent of all when you play a forcing club system; it is also the weak point of the bidding structure, because it gives the responder almost no information other than the fact that her partner has an opening hand.  It can be as short as a singleton.  The point count is 11-16 HCP and should be alerted as, "May be short."

Four Diamonds and Five Clubs
The opening bid is 1 when opener has both a 4-card diamond suit and also a 5-card club suit.  There's a bridge term that describes the auction where the second suit is longer than the first...   It's a Canapé bid.  All Big Club systems use this treatment.

Five Card Diamond Suit
Because an opening call of 2 shows a hand with a 5-card diamond suit and no 4-card major, the 1 bid denies that holding.  If the opening bid is 1 and opener later rebids the suit, she must also have an unspecified 4-card major that prevented her from opening 2.   (Responder will not usually know about the 4-card major until opener's second call.)

Treat your partner's 1 as semi-forcing.  You can pass with a weak hand, but only if you have at least four diamonds.  If you don't have that many, even with zero points, find a bid.  It's not going to be much fun for your partner to play in a 2-2 fit when she is looking at a zero-point dummy.

In general, if you have at least 7 points or more, the bidding will go rather normally.  Bid the way you have always responded to a minor suit opening by naming a biddable major.  What we need to discuss, though, are those very weak hands that are short in diamonds.

Consider this hand...    (And hope you never see it at the table.)
Three Card Heart Suit
At first glance, after learning that you should not pass with this garbage, you probably are thinking, "Okay, I guess I will bid 1."  Nope.  Don't even consider it!  Your response is 1 which your partner will alert and then tell the opponents that you might have a 3-card heart suit.

If your partner has a 4-card spade suit she will bid it and you can pass with a sigh of relief.  Hey, you are only at the one level.  The worst that will happen is that she might raise you to two hearts, but the 4-3 fit in hearts will probably be a better contract than diamonds.  Another thing...  you should not play support doubles for hearts, but it's okay for spades.

We have developed a set of agreements for Responding Over Our Diamond bid which we call ROOD.  It isn't perfect, but it's far better than not having an agreement!  This link has a complete description of this agreememt:   Responding Over Our Diamond

Below is a brief description of ROOD:
    NOTE:   Much of this agreement was developed by Lisa Walker
Major Suit Responses
Responder's bid of either 1 or 1 is alertable... It's Non-forcing and promises no more than 10 points.  Feel free to pass.

A jump to either 2 or 2 is forcing for at least one round, and promises a 5+card suit.  It also promises 11+ points.

One Notrump Response
This bid shows 11+ points, and may have one or both 4-card majors.  It's forcing for one round.  Opener rebids a major if she has one, and if she has both, she bids the heart suit first.  Bidding spades denies a 4-card heart suit.

Two Notrump or Three Notrump Responses
    If responder jumps to 2NT, the bid shows 5+5+ in the majors

    If responder jumps to 3NT, the bid shows 5+5+ in the minors

Responder's 3-Level Jump Bids
Most players today play that a Jump Shift by responder is a weak bid, but many expert level players are giving up on this treatment, and many are now using Soloway Jump Shifts showing a hand with at least 16 points.  Unfortunately, we don't get that sort of hand as often as we get 6-card suits with 8-10 points.  (It's the 6-8-10 hand.),
    A Jump Shift at the 3-level by responder, in any suit, shows at least a 6-card suit and 8-10 points
Responder Bids Two Clubs
This is "extended" ROOD... It shows at least 4-4 in the minors and is not forcing.  It's an attempt to find the best part-score.

Responder Bids Two Diamonds
This is also "extended" ROOD... It shows at least 4-5 in the minors and is forcing.  Usually it has 11+ points and a hand not suited for a 1NT response.  (Perhaps a major suit singleton or void.)
    See the web site's complete description of ROOD and Extended ROOD.