I-PETER(Intelligent Personalised English Tutoring EnviRonment):Modelling Personalised Diagnosis and Material Selection for an Online English Course .This system has been designed for the on-line distance learning of Englishwhere too many students restrict the teacher’s possibilities to provide individualised guidance. I-PETER is made up of four domain models that represent linguistic and didactic knowledge: the conceptual framework related to linguistic levels and knowledge stages, and the educational content and study strategies. The student model represents the knowledge that the student has learnt, thestudy strategies, and his/her profile. A student’s command of English is evaluated by interpreting his/her performance on specific linguistic units in terms of three related criteria, rather than by a general linguistic competence ranking. Evaluation consists of a diagnostic task model which assesses student performance, taking the form of a Bayesian network, and a selection mechanism that proposes appropriate materials and study strategies.