Johnson grass or Johnsongrass, Sorghum halepense, is a plant in the grass family, Poaceae, native to Asia and northern Africa. The plant has been introduced to all continents except Antarctica, and most larger islands and archipelagos. It reproduces by rhizomes and seeds.

Johnson grass has been used for forage and to stop erosion, but it is often considered a weed because:

Foliage that becomes wilted from frost or hot, dry weather can contain sufficient amounts of hydrogen cyanide to kill cattle and horses if it is eaten in quantity.

The foliage can cause 'bloat' in such herbivores from the accumulation of excessive nitrates; otherwise, it is edible.