Conjugated polymers, such as polyacetylene and polypyrrole, have attracted great attention since the discovery in 1977 of high electrical conductivity in doped polyacetylene. These polymers also exhibit important semiconductor properties at the intrinsic, undoped state. Electrochemistry has played a key role in the studies of conjugated polymers. In this chapter, we focus our attention on the electrochemistry of conjugated polymers, including electropolymerization to prepare the polymers directly from their monomers, the electrochemical properties of conducting polymers, and the electrochemical measurements of the HOMO and LUMO energy levels of conjugated polymers.