This thesis proposes to examine a practical aspect of the gong’an 公案 method of Chan 禪 Buddhist meditation, namely the nature and function of the “doubt sensation” or yiqing 疑情, as described in the yulu 語錄, or recorded sayings, of Foyan Qingyuan 佛眼清遠 (1067-1120), one of the earliest known exponents of this method. The thesis is divided into two main parts. After providing an overview of the related literature and of the way in which this topic has been dealt with previously, I analyse the subject of doubt in the recorded sayings of Foyan in Part I. An annotated translation of the key passages on the subject from the set of recorded sayings attributed to this Chan master is included in Part II. Auxiliary questions such as the transformation of doubt in the Chan school, the relation between faith and doubt in practice, and the interpretations of various scholars will also be considered with reference to this set of primary texts.