Production and processing of nori by current methods is a highly advanced form of agriculture. The biology of Porphyra, although complicated, is well understood, and this knowledge is used to control virtually every step of the production process. Farming takes place in the sea where the Porphyra plants grow attached to nets suspended at the sea surface and where the farmers operate from boats. The plants grow rapidly, requiring about 45 days from "seeding" until the first harvest. Multiple harvests can be taken from a single seeding, typically at about ten-day intervals. Harvesting is accomplished using mechanical harvesters of a variety of configurations. Processing of raw product is mostly accomplished by highly automated machines that accurately duplicate traditional manual processing steps, but with much improved efficiency and consistency. The final product is a paper-thin, black, dried sheet of approximately 18×20 cm (7.087×7.874 in) and 3 grams in weight.
There are several grades of nori available in the United States. The most common, and least expensive, grades are imported from China, costing about six cents per sheet. At the high end, ranging up to ninety cents per sheet, are "delicate shin-nori (nori from the first of the year's several harvests) cultivated in Ariake Bay, off the island of Kyushu in Japan."Like a fine wine, nori available only in Japan can cost up to US$50 per sheet.
In Japan, over 600 square kilometres (230 sq. mi.) of Japanese coastal waters are given to producing 350,000 tonnes (344,470 tons), worth over a billion dollars. China produces about a third of this amount.
Nori is commonly used as a wrap for sushi and onigiri. It is also a common garnish or flavoring in noodle preparations and soups. Nori is most typically toasted prior to consumption ("yaki-nori" in Japanese). A very common and popular secondary product is toasted and flavored nori ("ajitsuke-nori" in Japanese), in which a flavoring mixture (variable, but typically soy sauce, spices, and sugar in the Japanese style or sesame oil and salt in the Korean style) is applied in combination with the toasting process. Nori is also eaten by making it into a soy sauce flavored paste noritsukudani (海苔佃煮).
In addition, nori is sometimes used as a form of food decoration.
A related product, prepared from the unrelated green algae Monostroma and Enteromorpha, is called aonori (青海苔 literally blue/green nori) and is used like herbs on everyday meals like okonomiyaki and yakisoba.