  Blazars are the most common class of TeV extragalactic emitters. In the
framework of the AGN unified model, they are understood as AGNs with a
relativistic jet pointing close the line of sight. They are characterized by
extreme variability, observed to be as fast as minutes. These flares are
usually observed at multiple wavelengths and their study require fast reaction
and coordination among multiwavelength observatories. An important part of
blazars observations with the H.E.S.S. array of Cherenkov telescopes is thus in
the form of Target of Opportunity (ToO) observations. In this contribution the
H.E.S.S. blazar ToO program is presented, with a focus on recent results.
