  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.
