Submitted to ApJ Very high-quality spectra of 24 metal-poor halo dwarfs and subgiants have been acquired with ESO’s VLT/UVES for the purpose of determining Li isotopic abundances. The derived 1D, non-LTE 7 Li abundances from the Lii 670.8nm line reveal a pronounced dependence on metallicity but with negligible scatter around this trend. Very good agreement is found between the abundances from the Lii 670.8nm line and the Lii 610.4nm line. The estimated primordial 7 Li abundance is 7 Li/H = 1.1 − 1.5 · 10 −10, which is a factor of three to four lower than predicted from standard Big Bang nucleosynthesis with the baryon density inferred from the cosmic microwave background. Interestingly, 6 Li is detected in nine of our 24 stars at the ≥ 2σ significance level. Our observations suggest the existence of a 6 Li plateau at the level of logǫ6 Li ≈ 0.8; however, taking into account predictions for 6 Li destruction during the pre-main sequence evolution tilts the plateau such that the
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