Wagyu (Japanese: 和牛, Hepburn: wagyū, lit. 'Japanese cattle') is the collective name for the four principal Japanese breeds of beef cattle. All wagyū cattle originate from early twentieth-century cross-breeding between native Japanese cattle and imported stock, mostly from Europe.

Wagyu beef is among the most expensive meats in the world. It features marbling, meaning that streaks of fat exist within the red meat that make it tender and moist, while adding flavor. Wagyu beef is often known by different names depending on its place of origin. In several Japanese prefectures, Wagyu beef is shipped with an area name; examples include Matsusaka beef, Kobe beef from the Tajima cattle, Yonezawa beef and Ōmi beef. In recent years, Wagyu beef has increased in fat percentage due to a decrease in grazing and an increase in the use of feed, resulting in larger, fattier cattle.

Wagyu refers to "Japanese cattle" and is not a specific breed. Japanese native cattle became almost extinct after the Meiji Restoration (1868), mainly as a result of crossbreeding with European breeds, with exceptions such as the Mishima cattle. There are only a few hundred Japanese native cattle, and meat from these cattle is seldom sold on the market. Today, Wagyu refers to four breeds known as "improved Wagyu" (改良和牛, kairyō wagyū), which have been established as distinct breeds through crossbreeding with European cattle.

The rich marbling that is considered a characteristic of Wagyu is actually a feature of the Japanese Black breed, and not of the other three breeds. This is often misunderstood because the Japanese Black currently accounts for 97% of all Wagyu raised in Japan.

In 2001, bovine spongiform encephalopathy was reported in Japanese cattle and became a major social problem. Since then, stringent testing and registration measures for cattle in Japan have been implemented. Since 2007, only four breeds of kairyō wagyū and their crossbreds, as well as cattle born, raised, and duly registered in Japan, have been allowed to be labeled as Wagyu.

Western breeds such as Holstein and Jersey are also raised in Japan for dairy cattle. When meat from these cattle is sold in Japan, it must be labeled "domestic beef" (国産牛), not "Wagyu."

In 1927, fossils of an ancient wild species of cow, Hanaizumi Moriushi (Leptobison hanaizumiensis), dating from the Paleolithic period about 20,000 years ago, were discovered at the Hanaizumi Site in Ichinoseki City, Iwate Prefecture. The Hanaizumi Moriushi is a species similar to the bison and is said to be close to the steppe bison (Bison priscus) lineage. Fossil bones of Aurochs (Bos primigenius) have also been found in Ichinoseki City. Since Hokkaido and Honshu were land-locked with the Eurasian continent during the Ice Age, these animals came from the continent via Hokkaido.

In addition, projectile points made from polished wild cattle bones have been found at the same site, although in small quantities, suggesting that humans existed during this period and that Hanaizumi Moriushi and aurochs were hunted.