Administered at local centres in 120 countries throughout the world, IELTS (International English Language Testing System) is one of the most widely used large-scale ESL tests that also offers a direct writing test component. Because of its popularity and its use for making critical decisions about test takers, it is crucial to draw attention to some issues regarding the assessment procedures of IELTS. Therefore, the present paper aims to provide a descriptive and critical review of the IELTS writing test by focusing particularly on various reliability issues such as single marking of papers, readability of prompts, comparability of writing topics, and validity issues such as the definition of the "international writing construct", without considering variations among rhetorical conventions and genres around the world. Consequential validity-impact issues will also be discussed and suggestions will be given for the use of IELTS around the world and for future research to improve the test.