This research focuses on the contrastive analysis of authentic persuasive business correspondence written in English by Thai speakers and native English speakers in the Thai business context. Three types of persuasive correspondence - sales promotion, request, and invitation - were analysed from contrastive text linguistic and pragmatic perspectives. The purpose was to examine, compare and contrast their rhetorical structures, functions and linguistic realisations as well as persuasive and politeness strategies, and to compare these features to those found in textbook samples of persuasive letters in order to investigate the extent to which those samples represent the authentic, real-life correspondence. The findings report on cross-cultural variations which differentiate the persuasive writing patterns and strategies of Thais and native English speakers. Despite some shared writing conventions, the findings reveal diversity in some rhetorical moves, linguistic realisations, rhetorical appeals and politeness strategies. The diversity includes some cultural-bound discourse patterns and cultural-specific textual features, many of which can be traced to interference from the Thai language and culture. An exploration of the nature of sales promotion, request, and invitation letters presented in one American and two Thai textbooks on Business English writing reveals that their letter samples reflect the characteristics of the authentic corpus in the business contexts to which they belong. The implications of this research are twofold. First, it has implications for the teaching of English business letter writing especially in the Thai context and the innovation of more advanced materials and methods for this pedagogical purpose. Second, it raises an awareness of differences in persuasive writing across languages and cultures, worth noting for developing cross-cultural understanding and communication strategies for effective intercultural business interactions in the dynamic business environment of the 21st century.