The scanning tunneling microscope (STM) provide a sophisticated surface topographic imaging and analysis method in various environments. It has been well demonstrated that imaging graphite surfaces is possible with atomic resolution in air as well as in ultra-high vacuum. However, recent application of STM for samples immersed in aqueous solutions have suggested that STM might become a powerful tool for in-situ electrode surface characterization in the field of electrochemistry. Recent advances in STM in liquid systems are described in this article.