The very-high-energy (VHE, E>100 GeV) extragalactic sky is dominated by blazars, a class of active galactic nuclei which show rapid variability at all wavelengths. Target of Opportunity (ToO) observations triggered by flaring activity detected at longer wavelengths are thus an important part of the blazar observing strategy of H.E.S.S., an array of five imaging atmospheric Cherenkov telescopes sensitive to VHE photons.
In this contribution we detail the H.E.S.S. extragalactic ToO program, describing the specific procedures currently in place to follow up on multi-wavelength alerts.The program is illustrated by discussing a few recent noteworthy targets observed with the H.E.S.S. phase II array over the last two years of blazar ToO observations.