Your idea of casual might be flip-flops and a T-shirt, but that may not be what your host had in mind. If you're invited to a casual dinner party, remind yourself that the word "party" implies that the host expects you to show up looking festive. Always ask your host when you aren't sure what to wear, but plan on simple clothing that is polished without looking overdone.
What you wear to a casual dinner party depends on the time of year and where you live. A summer party in a beachy environment might involve Bermuda or cargo shorts, a polo or plain tee and sandals. If you're in the midst of a New England winter, opt for khakis or "nice" jeans and a button-down or sweater. Loafers, clean sneakers and other dress shoes are all footwear options.
A summery maxi-dress or skirt with a tank or short-sleeve top look appropriate in warmer climates. Dress shorts and a non-revealing top also work. In the winter, nice jeans or slacks with a blouse or sweater make a good looking but casual outfit. A casual wrap dress can span the seasons and geography -- and it always makes you look put together. Wear sandals, low heels or flats -- whichever goes best with your outfit choice. If you're concerned about being too underdone, stash a few easy-to-carry accessories -- such as a fancy scarf or flashy necklace -- in your purse so you can "change" at a moment's notice.
What Not to Wear
Even though the invite says casual, you should look like you put in some effort. Women should avoid clothing that's overly revealing or flashy. And men, leave the T-shirts with slogans and obvious workout attire at home. Don't confuse a casual dinner party with a formal one that usually requires a suit or tuxedo, and a fancy dress. You don't want to show up overdressed and out of place. If your invitation reads formal dinner party, follow an entirely different dressing protocol.