Phenolic compounds coexist in environmental samples and are toxic to animals and aquatic organisms. The rapid determination of phenolic compounds is an important environmental challenge. Electrochemical methods are the method of choice for sensitive, rapid, and precise determination of phenolic compounds. Electrochemical oxidation of phenols and chlorophenols and the use of electrochemical sensors as detectors in flow injection analysis produces enhanced selectivity, sensitivity, and reproducibility of determinations. Modification of conventional electrode surfaces is necessary in sensor constructions as they can be used as a sensing platform for phenols and chlorophenols. In this book literature reviews about properties of phenol and chlorophenols , use, environmental impact, and methods used in their determination are outlined. Description has been made about chemically modified electrodes, purpose of modification, preparation, types of modifiers and electroanalytical techniques. Experimental results have been discussed that include characterization of electrodes, parameter optimization, analytical performances and interference studies.