Indexing is the process of allocating index terms or keys to a record or document represented in an Information Retrieval System. Historically, the term indexing was applied to a human generated set of terms that could be used to locate an item (record or document). With the advent of computers and the availability of text in electronic form, alternatives to manual indexing are available and are essential to cope with the proliferation of information in the documentary form. Thus, automated techniques are absolutely necessary. In the case of manual indexing there are guidelines on the scope of indexing process. Such guidelines were necessary to ensure consistency as also to achieve the specific objectives of a particular indexing effort. The guidelines defined the level (depth) of detail to which the indexing was applied i.e., exhaustivity and specificity. The strength in manual indexing was the associative powers of human indexer in consolidating many similar ideas into a small number of representative index terms and knowing when concepts were of low value as not to warrant indexing. Automated indexing systems try to achieve these by using weighted and natural language systems and by concept indexing. It may be mentioned here that the reliance of automated systems on statistical information alone will not be able to achieve accurate assignment of importance and weights to concepts that are being indexed. Therefore, it is important to develop algorithms for automatic indexing. In other words, a computer can select index terms in accordance with a set of instructions. Selection will depend upon word occurrence. The index terms that may be assigned are drawn from a standard list or computerised thesaurus, on the basis of word occurrence in a record or document. An alternative method is to arrange manually assigned index terms alphabetically. Such terms will be selected and assigned by the indexers on the basis of indexer's subjective assessment of the content of the document. In either case, computer acts as a tellable tool for arranging as well as displaying of the index terms.