Hadronic contributions to a_μ below one GeV

I present a method for evaluating the hadronic vacuum polarization contribution below 1 GeV to a_\mu which relies on analyticity, unitarity and chiral symmetry, as well as on data. The main advantage is that in the region just above threshold, where data are either scarce or have large errors, these theoretical constraints are particularly strong, and therefore allow us to reduce the uncertainties with respect to a purely data-based evaluation. Some preliminary numerical results are presented as illustration of the method.