Direct chlorination of 1-CH3-CB11H11- in glacial acetic acid gave the highly chlorinated carborane anion 1-CH3-B11C11-, and treatment of 1-CH3-CB11H11- with ICl in triflic acid afforded the highly iodinated carborane anion 1-CH3-CB11I11- Under similar or more vigorous reaction conditions, however, the reaction of 1-CH3-CB11H11- with Br-2 in triflic acid did not proceed to completion. The highly brominated carborane anion 1-CH3-CB11Br11- was achieved via a sealed-tube reaction. This new method has led to the isolation of 1-H-CB11X11- (X = Cl, Br, I) and 1-Br-CB11Br11- in high yield. The lithiation of 1-H-CB11X11- resembles that of its parent anion CB11H12- Treatment of these lithio species with methyl iodide gave the methylated carborane anions 1-CH3-CB11X11- These new weakly coordinating anions were fully characterized by H-1, C-13, and B-11 NMR, IR, and negative-ion MALDI MS spectroscopy. Some were further confirmed by single-crystal X-ray analysis.