  We present a comprehensive analysis of deep inelastic scattering from He-3
and H-3, focusing in particular on the extraction of the free neutron structure
function, F_2^n. Nuclear corrections are shown to cancel to within 1-2% for the
isospin-weighted ratio of He-3 to H-3 structure functions, which leads to more
than an order of magnitude improvement in the current uncertainty on the
neutron to proton ratio F_2^n/F_2^p at large x. Theoretical uncertainties
originating from the nuclear wave function, including possible non-nucleonic
components, are evaluated. Measurement of the He-3 and H-3 structure functions
will, in addition, determine the magnitude of the EMC effect in all A < 4
nuclei.
