Generally, language teaching is a very complex discipline. Analyzing the ESP branch of the tree, we can see three main subcategories, i.e. EST – English for Science and Technology, EBE – English for Business and Economics and ESS – English for the Social Sciences. Furthermore, each of these categories is yet divided even further, i.e. EAP – English for Academic Purposes and EOP- English for occupational Purposes. We have to bear in our mines that EOP is actually, higher than EAP, which of course, has nothing to do with their importance, but it refers to the fact that EOP can be diversified even more, according to the individual occupational needs.
The Tree of ELT certainly does not suggest that any of the levels of the tree should be considered more important than the others. Hutchinson and Waters state what ESP is not, rather than it is:
a)   ESP is not a matter of teaching, specialized varieties of English. The fact that language is used for a specific purpose does not imply that it is a special form of the language, different in kind from other forms. There are some features which can be identified as, typical of a particular context of use and the learner is more likely to meet in the target situation. b). ESP is not just a matter of Science word and grammar for Scientists, Hotel word and grammar for Hotel staff and so on. We need to distinguish, as Chomsky did with regard to grammar, between performance and competence that is between what people actually do with the language and the range of knowledge and abilities which enables them to do it (Hutchinson and Waters, 1981). c). ESP is not different in kind from any other form of language teaching. (Hutchinson and Waters, 1993, 18).
What is ESP?
ESP is a kind of English which relates to learner’s professional or personal needs, somewhat modulating the General English curriculum extent. The General English curriculum teaching deals mainly with teaching the language system, whereas the English for Specific Purposes teaching focuses rather on how the language is used in a real discourse.
Course design is the process by which information about learning needs and learning theories is interpreted to produce materials depending on syllabus to develop methodology for teaching to establish evaluation procedure in order lead the learner to detain the state of knowledge. Robinson (1991) stated that course design refers to the planning and structuring of a course to achieve the needed goals. There are the result of the needs analysis, the course designer’s approach to syllabus and methodology, and existing material. An approach to language teaching which aims to meet the needs of particular learners. It means that in practice that much of the work done by ESP teacher is concerned with designing appropriate courses for various group of learners, in order to provide a reasonable basis for the subsequent processes of syllabus design, materials writing, classroom teaching and evaluation.It is important to concern on 5W+1H question to know the whether  proceesses are reasonable or not. This all question should include the three main headings namely: language description, theories of learning, and need analysis.
The language description is the way in which the language system is broken down and describe for the purpose of learning. The terms such as ‘structural’, ‘functional’, ‘national’ properly belong to this area, those refer to the way of analyzing and describing a language. in the area of learning theories, the relevant term we shall consider are ‘behaviorist’, ‘cognitive’, ‘affective’.
Need analysis is generally regarded as a criterion to the ESP. Conducting the need analysis is a one of essential stage in the ESP since it will determine how our ESP course is, in term of teaching material, learning situation, teaching methodologies, and evaluation. Besides, by doing the need analysis, the teacher will get two kinds of information which first is the students’ current level of knowledge and motivation, and the second is the students’ need.
There are management issues that include the timing and location of the proposal course, the teacher and facilities available, and the time available for planning. The first issue is the timing, in this case the timing and indeed the timeable of the course may not be negotiated. It may dictate the nature of some teaching activities, for example if the class sessions are infrequent (once a week), each session may need to be treated as self-contained, with no carry -over expected from one week to the next. The second is the location, an important consideration is the location of the course. The nature of the classroom and their distance from the student’s other places of work may influence the decision which related to the syllabus and even more the methodology. In the ESP course, the location can be in a school and in the company. Those usually done based on the contract with the sponsor. The last specific issue is the facilities, for example a sufficient and a good typist and functioning photocopying machines. It will support to create an effective learning condition. The facilities should be based on the students’ need and also up to date.