Dumplings mean different things depending on where you are and the kind of meal you are having. One kind of dumpling goes into soups and dishes such as chicken and dumplings; the other kind is the steamed or fried Chinese dumpling filled with meat and vegetables. Soup dumplings don't necessarily need cornstarch; Chinese dumplings, on the other hand, need cornstarch at a few crucial points in their preparation.
More Starch Please
Cornstarch, which is starch that comes from the flesh inside the corn kernel, is typically a thickening agent in soups, stews and sauces, but it is also a key ingredient in dumpling creation and preparation. Adding cornstarch to the dough, which can often be as simple as flour mixed with water, will make the dough firmer and chewier. Cornstarch also helps the dumpling's fillings stick together. Some recipes made with packaged dumpling wrappers instead of homemade dough call for you to make cornstarch into a slurry, which is then added to the wrappers' edges to help the edges bind together.