Essay-based examinations form a cornerstone of the public assessment system in the UK, but comparatively little research has been conducted into the processes involved in designing, answering and appraising essay-based questions/responses. This study explores the idea of examination validity through a qualitative review of these processes, based on materials sourced from the June 2002 OCR Politics AS/A2 module 2596 (Politics of the UK). Through a detailed analysis of question papers and candidate scripts (informed by mark schemes, curricula and examiner reports), a model of current processes is advanced. Issues related to question design are highlighted, and a methodology for future quality assurance in essay-based examinations is derived from philosophical considerations such as "fairness" and "validity". This paper resulted from research conducted as part of the University of Cambridge Local Examinations Syndicate's ongoing work to develop a system of procedural guidelines and example questions to facilitate robust question design.