The synthesis of well-defined poly (ionic liquid) brushes with tunable wettability using surface initiated atom transfer radical polymerization (ATRP) was reported. Various characterization techniques including ellipsometry, static water contact angle measurements, attenuated total reflection infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) were used to characterize the films for each surface modification step. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from the surface was a controlled process with a "living" characteristic. Furthermore, the surface of poly (ionic liquid) brushes with tunable wettability, reversible switching between hydrophilicity and hydrophobicity can be easily achieved by exchanging their counteranions.