The general aim of the research presented in this thesis is to extend the application of microstructural and microchemical analytical techniques, with the longer term objective of better informing textile conservation. The ability to identify the components of threads in historic textiles and characterise their state of degradation is essential when considering potential conservation treatments. Three particular constituents are considered here, namely metals, and plant and silk fibres. Metal threads are found in wide variety of historically important textiles, and their composite nature can complicate characterisation and treatment. Examples from a range of sources were assessed by a range of microscopic and spectroscopic techniques. It was demonstrated that these approaches allowed the determination of the general type, composition, state of degradation and likely methods of manufacture of these materials. In addition, investigations of metal threads from two specific artefacts were performed: the Jesse Tapestry, a 15th century ecclesiastical hanging; and a piece of 19th century embroidered artwork, produced in the style of the 17th century. Cellulosic fibres can prove difficult to distinguish due to their similarities in composition and structure. The work presented here describes the development of an ATR FT-IR spectroscopic technique for the characterisation of six species of commonly encountered plant fibres, using linear discriminant analysis on peak intensity ratios, to allow differentiation on the basis of characteristic lignin and cellulose contents. Further investigations using a polarised ATR technique allowed the fibre microstructure to be probed, permitting further distinction, for example of hemp and flax, on the basis of the characteristic angles and senses of winding of the cellulose fibrils. Metal weighted silk fibres, found in many important artefacts, are particularly susceptible to deterioration and so are a special area of concern. The research has concentrated on developing a micro-methodology to assess these materials, and specifically to identify spectroscopic signatures that correlate to physical properties. In order to do so, samples of habutae silk were weighted, using historically accurate methods, then aged by means of either elevated temperatures or intense illumination. Physical properties were assessed by measurement of breaking strength and Young's modulus. Subsequently TGA, HPLC, UV/Visible and ATR analyses were carried out. A good correlation was found between the physical state of the fibres and both the retention time of the major silk peak (measured in the H P L C experiment) and an orientational order parameter (derived from the pol-ATR data).