Hyssop is a brightly coloured shrub or subshrub that ranges from 30 to 60 cm (12 to 24 in) in height. The stem is woody at the base, from which grow a number of upright branches. Its leaves are lanceolate, dark green, and from 2 to 2.5 cm (3⁄4 to 1 in) long.

During the summer, hyssop produces pink, blue (ssp. aristadus), or, more rarely, white fragrant (ssp. f. albus) flowers. These give rise to small oblong tetra-achenes.