Abstract I. Introduction 108 II. Structural Analysis 109  III. Copolymer Composition 111 A. Composition by the Direct Method 111 B. Composition by the Method Based on Statistics 111 C. Copolymer Composition by the Hard‐Ionization Method 113 IV. Copolymer Sequence 114 V. Molar Mass Determination 115 VI. MS as a Detector for Liquid Chromatography 116  VII. Composition Drift and the Compositional Distribution Histogram 120 VIII. Quantitation and Methods to Correct Mass Spectral Intensities 121 IX. Copolymer Mixtures and Blends 122 X. Copolymers Obtained by Specific Synthetic Routes 123 A. Copolymers Produced by Enzymes or Occurring in Nature 123 B. Block Copolymers 125 C. Random Addition Copolymers 126 D. Random Condensation Copolymers 128 XI. Summary and Outlook 133 Acknowledgments 134 References 135 Recent and older literature (covering the last 12–13 years) in the field of mass spectra of random and block copolymers is reviewed. A detailed description is given of the information on copolymer properties that can be recovered from the analysis of the low‐mass region of the spectrum (the region below 500 Da) and the high‐mass region. The features of mass spectra of copolymers obtained by different synthetic routes are discussed, such as free radical, condensation, ring‐chain equilibration, microbial synthesis, ring‐opening, simple anionic, cationic, Ziegler‐Natta, and/or metallocene catalysis, along with some random and block copolymers that occur in Nature. The emphasis is on copolymer composition and average molar mass determination, and on the benefits of coupling mass spectrometry (MS) with separation techniques such as size‐exclusion chromatography (SEC) and high performance liquid chromatography (HPLC). © 2002 Wiley Periodicals, Inc., Mass Spec Rev 21:108–144, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mas.10021