Basic purpose of this article is to Discuss on the Theory of Substitution Effects. Here focus on Ring Activation and Ring Deactivation. Ring activators are groups that enhance the electron density on the benzene ring and thereby make the ring more susceptible to electrophilic aromatic substitution reactions. Ring deactivators decrease the electron density around the benzene ring, thus creating the ring less reactive when it comes to electrophilic aromatic substitution reactions. Resonance theory can be used to illustrate these procedures.