This article is part of a larger scale project on some aspects of the process of academic socialization of a group of Iranian Ph.D. students studying in five UK universities, particularly focusing on the relationship between these students and their supervisors. The study included eight engineering and five social sciences/humanities students, as well as four engineering and two social sciences/humanities supervisors. The overall methodology of the study has been a constructivist version of grounded theory, which is based on a rigorous approach to working with qualitative data and a constructivist epistemology according to which the results of the study are not "realities out there" but the result of the interaction between the researcher and the data. This study looks at the relationship between students and supervisors as legitimate peripheral participation. The main features of this are that novice members are given enough credibility to be considered as "legitimate" members of their target communities and are given "less demanding" practices to perform to learn the craft of their "masters". It is argued that this concept is a productive tool to understand the nature of learning at the Ph.D. level, but it is realized differently in various fields of study. It is also argued that legitimate peripheral participation is in line with informal routes to learning, an aspect which seems to be partially ignored in recent Ph.D. training guidelines by the Economic and Social Research Council.