Physical and spectroscopic methods have been used jointly for characterization of polymers for at least four decades. Yet, new techniques permit increasingly refined determination of polymer chemistry and morphol­ ogy_ The correlation of this knowledge with physical properties of polymers is helpful to planned synthesis of new products. The most prominent spectroscopic techniques through the forties and fifties were infrared and ultraviolet spectroscopy. Nuclear magnetic resonance, electron spin resonance and MOssbauer spectroscopy started making sig­ nificant contributions to polymer chemistry in the early sixties. Still more recently fluorescence spectroscopy and laser Raman spectroscopy have become readily appli­ cable to polymers and are contributing significantly to the understanding of the relationship between polymer structure and properties. Determination of the distribution of monomer se­ quences by molecular size has become possible through combined gel permeation chromatography and spectroscopic analysis. Fragments of polymers from chemical break­ down or from pyrolysis are further fractionated and structurally analyzed. The relationship between the chemistry of polymers and performance can be determined from changes in chemical structure and orientation after curing, degradation, or physical or thermal manipulation of the polymers.