In this short article, Rob Vanhoff looks at the teaching of Lunar Sabbath. Those who advocate this theory suggest the Sabbath is reckoned by the moon. Therefore, the Sabbath does not fall on a Saturday, but rather changes according to the moon’s cycle. Vanhoff shows that for such a theory to be true, Israel would have had to undergone “collective amnesia.” Furthermore, Vanhoff shows that the Tanach itself does not support such a theory. Consequently, Vanhoff shows this teaching to be false.