Alkali-soluble resins (ASRs) are random copolymers that contain both hydrophobic groups and a large number of carboxylic acid groups, which are widely used as the sole stabilizers in the production of waterborne dispersed polymers because they remarkably improve the end-use properties of the latexes. However, they reduce the radical entry rate. In this work, the mechanisms for radical entry in ASR-stabilized systems have been investigated. It has been found that the mechanism responsible for the reduction of the rate of radical entry depends oil the type of ASR used (prone or not prone to suffer hydrogen abstraction), the type of radical produced from the initiator (charged or uncharged, oxygen centered or carbon centered), the phase where the radicals are produced (aqueous or oil phase) and the type of monomer (hydrophobic like styrene or more hydrophilic like methyl methacrylate).