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The characterisation of materials composing objects of museum collections is vital for understanding the degradation mechanisms affecting them. Polymers of either natural or synthetic origin constitute a widespread class of materials commonly found in these objects. Although natural polymers have been the subject of several studies, aspects about their reactivity and degradation are still not fully understood. Synthetic polymers have been more recently introduced in collections, causing new and complex conservation issues to arise. Over the last decade, Attenuated Total Reflection (ATR)-FTIR spectroscopic imaging has emerged as a powerful method for the analysis of a broad range of materials. FTIR spectroscopic imaging utilises a Focal Plane Array detector (FPA) that reveals the spatial distribution of the compounds on the micrometre scale. Besides, this method is inherently non-destructive to the sample/objects analysed. However, the application of the ATR-FTIR spectroscopic imaging approach in conservation science has been limited and its great potential has yet to be fully realised. The aim of this thesis was to investigate degrading polymers in selected historical samples and objects of museum collections with both macro and micro ATR-FTIR spectroscopic imaging. The macro ATR imaging set-up revealed new insights into the degradation of these samples, such as the formation of calcium soaps both in parchment and leather book covers. Micro ATR-FTIR spectroscopic imaging allowed a deeper understanding of mechanisms affecting the stability of cellulose nitrate items to be obtained. For the first time, depth profiling analysis of these polymeric materials using custom-designed apertures with both macro and micro ATR-FTIR spectroscopic imaging was applied. Depth profiling with micro ATR-FTIR imaging detected evidences of the degradation of plastic objects beneath the surface, without complex sample preparation steps. Furthermore, as with this method anomalous dispersion causing shift of strong bands in ATR spectra can be reduced, it aided the assignment of specific spectral bands of components in historical leather and parchment. The results obtained provide useful information to improve methods for preserving objects of cultural heritage.