Wasabi (Japanese: ワサビ, わさび, or 山葵, pronounced [waꜜsabi]; Eutrema japonicum or Wasabia japonica) or Japanese horseradish is a plant of the family Brassicaceae, which also includes horseradish and mustard in other genera. The plant is native to Japan and the Russian Far East including Sakhalin, also the Korean Peninsula.^: 133 It grows naturally along stream beds in mountain river valleys in Japan.

It is grown for its rhizomes which are ground into a paste as a pungent condiment for sushi and other foods. It is similar in taste to hot mustard or horseradish rather than chili peppers in that it stimulates the nose more than the tongue, but freshly grated wasabi has a subtly distinct flavor.^: 53 The two main cultivars in the marketplace are E. japonicum 'Daruma' and 'Mazuma', but there are many others.

The oldest record of wasabi as a food dates to the 8th century AD. The popularity of wasabi in English-speaking countries has coincided with that of sushi, growing steadily starting in about 1980. Due to issues that limit the Japanese wasabi plant's mass cultivation and thus increase its price and decreased availability outside Japan, the western horseradish plant is generally used in place of the Japanese horseradish. This version is commonly referred to as "western wasabi" (西洋わさび) in Japan.