Methylboronic acid and ita anhydride, tximethylboroxin, were prepared by three routes. The carbonylation of borane-dimethyl sulfide gives in high yields trimethylboroxin, readily hydrated to methylboronic acid. The reaction of methyllithium with selected trialkoxyboranes and methyl Grignards with 2-methoxy1,3,2-&0xaborinane yields the corresponding esters, readily hydrolyzed to methylboronic acid in good yields. Methylboronic acid can be dehydrated to trimethylboroxin. Each of these routes was studied in detail to develop efficient, relatively simple routes to both methylboronic acid and trimethylboroxin.