ROME — A nattily dressed gentleman, unlit cigar poised between his lips, studies the pastas in a soccer-field-length supermarket aisle. Signore Pino Magno is an Italian diplomat who loves to cook. He is choosing pasta to go with one of his sauces. After much consideration, Magno decides on a bag of casarecce, a delicately once-twisted, short shape with a channel running down its center. This crevice will allow the sauce to seep deep into the cooked casarecce. His wife, standing patiently nearby, explains that he does this all the time. There are, after all, hundreds of shapes from which to choose.

We may not have the choices available in Italy, but gone are the days when only spaghetti, macaroni, and lasagna were available, and when brands in our markets only offered American-made noodles. Now we have popular Italian pastas made by Pastene, De Cecco, Barilla, and Delverde, along with artisanal and regional pastas. Gone, too, is the notion that sauces are made from tomatoes, cream, or pesto. Now there are dozens of mixtures to toss with your noodles.

Giancarlo Sessa, owner for 25 years of Sessa’s Italian Grocery in Somerville’s Davis Square, recently started counting pasta shapes in his store. He got up to 58 — for one brand, Del Verde — and quit halfway through his inventory. Stacked and unopened boxes of specialty cuts (these are unusual pastas such as the short, giant tubes called tuffoloni, also called paccheri, or the casarecce that Magno was interested in) lay waiting to claim space on his shelves. Rattling off the names of his pastas in order of size and shape, he stopped to ask: “Sounds like an Italian opera, doesn’t it?” Good pasta is made with durum wheat, semolina, and water (often spring water). Pastas are graded in small increments of thickness; they are smooth or ridged, tubular or flat. They come boxed in nests or packaged in elongated parcels. Specialty cuts are contorted in twists, shaped like little ears, made with squid ink or spinach. Different manufacturers call the same pasta shapes by different names. Neighboring Italian villages might not even agree on the same name.

But that’s just half the confusion. What about the sauce? Like shapes, the types of sauces familiar to Americans have expanded in recent years. Pairing pasta and sauces takes into consideration the heft of the sauce and size and texture of the pasta, along with regional preferences.

Tubular pastas such as ziti, rigatoni, and penne, which hold sauces in their cavities, are often paired with long-cooked red sauces, as well as savory mixtures simmered with chunks of meat and vegetables. The ribbed (rigati) tubes are more roughly cut, and the sauce seeps into the ridges. They are sturdy enough to hold up in a baked dish. The smooth (lisci) ones work well with oil and cream-based sauces that cling to the surface.

Long, flat linguine, fettuccine, and tagliatelle have enough surface area to hold thick tomato sauces, as well as pesto, cream, and oil-based seafood mixtures. Because long, round shapes — from spaghetti to angel hair — vary in thickness, toss thinner pastas with light sauces, perhaps made from fresh tomatoes; thicker ones stand up well with red or creamy carbonara sauces.

Known as soup pasta, tubettini, mini shells, ditalini, pastina, and rice shapes cook quickly. Any starch emitted during simmering thickens the pot. Some, such as pastina and stellina, are suited to simple broths, while thicker shapes such as ditalini and little shells go well in minestrone and pasta e fagioli (pasta and beans).

Stuffed pastas, like the folded tortellini and tortelloni from the Emilia Romagna region, which are filled with cheese and meat or vegetables, can also be served in broth with a sprinkling of cheese. Their more robust southern cousin, ravioli, is often bathed in tomato sauce.

The only thing more important than matching shape to sauce is cooking the pasta correctly. Use the cooking times on packages as a guide. Many Italians cook it for one to two minutes less than the instructions, then they finish cooking the pasta in the sauce. That way, you get “al dente” pasta — or strands that are tender “to the tooth.” The pasta absorbs the liquid as well as its flavors. Another tip is to save about half a cup of the pasta cooking liquid before draining. Add it to the pasta after draining it. If you stir over low heat, the sauce will give the pasta a shiny coating. Finally, never rinse pasta; you wash away flavor.

In Italy, and for many Italian-Americans here as well, pasta is always on the menu for midday Sunday dinner.

Maria and Tony D’Itria of Revere, who come from a town south of Naples, make pasta together every week. “I make fusilli just like my grandmother,” says Maria D’Itria, an elementary school teacher in Boston. “They are as big as your thumb and look like Shirley Temples curls.” One week recently the D’Itrias made rabbit and tomato sauce, which gets trapped between the curls of the pasta. “Americans put too much sauce on their pasta,” says Maria D’Itria. “The sauce should be just as though it is painted on.”

In Rome, Pino Magno’s casarecce might be on its way home, where it will be cooked slowly with a sauce made from zucchini and broth. Magno will probably return to the same store soon, pick another shape, and match it to another pot of sauce, while his wife waits patiently again.