This chapter discusses difficult airway, causes of difficulty, patient factors, and types of difficulties. One of the principal difficulties in predicting airway problems under anaesthesia is that in most unexpected cases there are no symptoms. The symptoms associated with obstructed sleep apnoea (OSA) syndrome should be sought in suspected cases. Anaesthetists should be aware of the symptomatology (and signs) of impending airway obstruction. The chapter briefs about special investigations such as 'Quick look' laryngoscopy, ultrasound and radiology. Sleep apnoea patients in particular may well be at greater risk in the postoperative period than at induction, whilst some types of surgery are notorious for engendering airway difficulty post-operatively; facio-maxillary and anterior cervical surgery are examples. Rheumatoid and acromegalic diseases of the larynx are particularly prone to post-extubation obstruction, so that the smallest possible size of tracheal tube should be used.