This study applies Halliday s Systemic Functional Grammar to text analysis. The readability of Technical English in Norwegian-produced, English as Second Langugage textbooks has been assessed in terms of its discourse organisation. This is done by undertaking an analysis of the Theme-Rheme/thematic structure and relating it to the Given-New/information structure. Texts produced by Norwegian writers have been compared with those by English writers. From these analyses, the thematic patterns and thematic progression were developed, and together with Theme choice, form a picture of discourse organisation that shows the textuality and coherence of a text. The results indicate that there are differences in discourse organisation between texts produced by Norwegian writers and those by English writers. Due attention to Theme choice and thematic progression by Norwegian writers would enhance the discourse organisation and hence the text s readability.