Direct measurement of the ground-state dissociation energy of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Na</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

We report a direct measurement of the ${\mathrm{Na}}_{2}$ $X^{1}\ensuremath{\Sigma}_{g}^{+}$ ground-state dissociation energy. Three spectroscopic measurements are combined to directly yield the energy of the lowest ($v=0$) vibrational level relative to the free-atom limit. The $X^{1}\ensuremath{\Sigma}_{g}^{+}(v=0\ensuremath{\rightarrow}31)$ splitting is measured by double-resonance spectroscopy; $X^{1}\ensuremath{\Sigma}_{g}^{+}(v=31)\ensuremath{\rightarrow}A^{1}\ensuremath{\Sigma}_{u}^{+}({v}^{\ensuremath{'}}=165)$ by laser-induced fluorescence; and free $\mathrm{atoms}\ensuremath{\rightarrow}A^{1}\ensuremath{\Sigma}_{u}^{+}({v}^{\ensuremath{'}}=165)$ by photoassociation of ultracold atoms. The result is ${D}_{0}=5942.6880(49)$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The uncertainty is a factor of 6 improvement over a previous (indirect) determination.