Sometimes when partner opens a minor you have no 4+ major suit to show and no fit with partner’s minor. As always with minors, you are probably going to want to play in NT so you can tell your partner that, and give them an indication of how strong your hand is by bidding the appropriate number of NT, as shown in the panel above.

There are times when you might want to respond 1D over 1C instead of bidding NT (for example if you have a nice diamond suit and a good hand) or to take some other action if your right hand opponent bids a suit where you don’t have a stopper.  This might be to pass with a weak hand or make a takeout double with a better hand.