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.