SUMARY The present dissertation deals with the notion of reformulation and with a group of lexical units by means of which the activity of reformulation is codified and explicitly signaled in the language. These lexical units will be referred to as DISCOURSE MARKERS of REFORMULATION or REFORMULATORS. The area of reformulation and of English reformulators is still an uncharted and unexplored territory. Thus, it was necessary to first provide an adequate definition of the notion of REFORMULATION in the English speaking-world that would allow me to lay the foundations for the detailed study of a group of lexical units that display a reformulative function in English. Secondly, I elaborated a justified taxonomy of English Discourse Markers of Reformulation along with their classification into different groups and sub-groups on the bases of the type of reformulation effected on the previous discourse segment or S1. Next, once Discourse Markers of Reformulation were defined, their properties ascertained and their sub-classes outlined, the groups of Explanation (that is to say, in other words, in simpler terms, in more technical terms, viz., namely, for example and for instance) and Rectification (or rather, [or] more precisely-accurately, [or] better still-yet) were analyzed in detail and the SYNTACTIC, DISTRIBUTIONAL PROPERTIES, PRAGMATIC FUNCTIONS and DOMAIN OF USAGE of the reformulators identified. With the assessment of all these properties it was my aim to delimit their ENVIRONMENTS OF USE and to obtain a principled description of them, both individually and as a group. Finally, reformulators of Explanation and Rectification were submitted to a test of SEMANTIC SUBSTITUTABILITY where replacement of one marker, A, for another, B, that did not occur in As original environment, was accounted for. The results obtained from this test allowed me to organize the taxonomy of English Discourse Markers of Explanation and Rectification into a hierarchy of HYPERNYMS, HYPONYMS, EXCLUSIVE USES and SYNONYMS. In this respect, my aim was to help to broaden our knowledge of how these lexical units behave in English and to come up with a clear picture of two groups of English reformulators.