By the mid-1900s, the impact of behaviourism and linguistic structuralism had led, in the area of second/ additional language teaching, to the development of structural syllabuses and audio-lingual methodology. It was not long, however, before both behaviourism and full-blown linguistic structuralism began to be challenged, challenges which underpinned a raft of proposals relating to both methodology and syllabus design. In some cases, the distinction between syllabus and methodology has become blurred to such an extent that it has been suggested that any attempt to differentiate between the two is irrelevant or even, perhaps, misguided. There can be few who do not accept that the interaction between the what (content) and the how (methodology) of language teaching is a critical one. This should not, however, mean that any research that focuses on the content of language courses is no longer relevant. Even so, while there is a considerable body of research that relates primarily to methodology, there is much less that relates primarily to syllabus. It is with issues relating to the language syllabus that this thesis is concerned. More specifically, it explores the impact that a range of syllabus design proposals has had, directly or indirectly, on a sample of English language textbook writers and English language teachers. One part of the research programme reported here focused on English language teachers and language programme managers operating in the tertiary education sector. A sample of English language teachers who completed a questionnaire-based survey were found, in general, to favour clearly articulated blended syllabuses that include a primary focus on vocabulary and grammar and, to a lesser extent, discourse features. However, there was considerable disagreement about the nature of the content that is appropriate at different levels and evidence of a high degree of uncertainty and confusion in the area of achievement objectives setting and discourse-based specifications. In addition, approximately one third of the respondents reported that they relied heavily on commercially produced textbooks in determining the detailed content of the language courses for which they were responsible. A sample of language programme managers/ co-ordinators who participated in semi-structured interviews all stressed the importance of having explicit syllabuses for the courses and programmes offered by their institutions. Grammar, tasks, vocabulary, language skills and learning skills were each considered to play an important role in General English (GE) courses, and skills and discourse features were considered fundamental in the case of English for Academic Purposes (EAP) courses. In only one case, however, did the programme documentation provided by the interview participants include a reasonably clear indication of course content and, once again, as in the case of the teachers who took part in the questionnaire-based survey, there was evidence of considerable reliance on commercially produced textbooks in determining detailed course content. In another part of the research programme, representative samples of widely used, commercially produced textbooks focusing on GE or EAP were analysed from the perspective of the nature of the syllabuses underpinning them. So far as the GE textbooks are concerned, it was found that the structural syllabus was becoming situationalized and lexicalized by the mid-1960s, with indications of incipient functionalization emerging in the early 1970s. Some attempts to design textbooks around a more wholly functional syllabus in the late 1970s and 1980s appear to have been largely abandoned by the 1990s. By that time, the syllabuses underpinning GE textbooks were found to have a largely situationalized and functionalized lexico-grammatical core. From the 1990s onwards, there was an increasing focus on skills (including learning skills), with a limited range of discourse features being added to the mix, yielding a more complex type of hybrid syllabus. With very few exceptions, the writers of commercially available GE textbooks appear to have shown little enthusiasm for syllabuses that are primarily lexical, task-based or relational in orientation. In the case of the EAP textbooks, the underlying syllabuses were found to be largely discourse-based, the primary emphasis being on cohesive devices and, to various extents and in varying combinations, paragraphing, generic cross-disciplinary organizational structures (e.g. general/ particular and problem/solution) and a variety of text-types and discourse modes. While some textbook writers appear to have accommodated the different strands of what are essentially hybrid syllabuses with little difficulty, others appear to have been less successful in doing so, leading to a somewhat disjointed, even haphazard approach to syllabus specification. While several proponents of different approaches to syllabus design have tended to reject other approaches out of hand, textbook writers and language teachers appear, in general, to have opted for a compromise position. However, that compromise appears to have been, at times, an uneasy one, one that can result in syllabuses that are neither coherent not theoretically grounded.