Production of increasingly sophisticated functional macromolecules and development of new polymerization processes have placed a severe demand on analytical methodologies for accurate characterization of synthetic polymers. With regard to the variety of heterogeneities found in polymer samples, where molecules can be distributed in terms of molar mass, chemical composition, functionality, molecular architecture, and concentration, development of multidimensional approaches is mandatory. The large orthogonality of liquid chromatography (LC) and mass spectrometric (MS) techniques, both largely employed individually in the field of synthetic polymers, makes their coupling very attractive. Because of its unrivaled softness that ensures molecule integrity upon ionization and of its ability to accommodate a flowing liquid, electrospray is the ideal ionization source to interface them. However, the electrospray process also raises some constraints on the composition of the liquid phase from which molecules have to be transferred in the gas phase as ions to be mass detected. This article reviews the capabilities and limitations of various on‐line LC‐ESI‐MS couplings involving most commonly used chromatographic techniques for synthetic polymer separation in the liquid phase, namely size‐exclusion chromatography (SEC), liquid chromatography at critical conditions (LCCCs), and gradient polymer elution chromatography (GPEC).