This study aims to provide scholars with insight into the task of writing research articles. Research questions: (1) What are the generic structures of research article introductions in three engineering subdisciplines? and (2) What are variations that distinguish the introductions of one subdiscipline from the others? Literature review: Swales's genre analysis method has proved to be an effective textual analysis to identify the structural organization of each section of research articles. Even though there seems to be a pattern in each section, previous genre-based studies also demonstrate that disciplinary variation is discernible. It thus remains to be determined whether research articles of different subdisciplines within a single discipline share the same organizational structure. Methodology: Based on journal impact factors, three datasets of English research article introductions representing three subdisciplines of engineering (civil, software, and biomedical) were compiled, consisting of 180 introductions with 60 from each subdiscipline. Then, the three datasets were analyzed using Swales's genre analysis technique to identify the structural patterns prevalent in the introductions of each subdiscipline. Units of textual analysis called moves and steps were quantified to capture variations among the introductions. Results and discussion: Analysis shows that these introductions generally adhere to a common rhetorical organization across subdisciplines. However, disciplinary variations are also captured, highlighting the unique characteristics and perspectives of each subdiscipline. The findings bear pedagogical implications, allowing English for Specific Purposes practitioners to prepare novice scholars to be able to publish successfully in their fields.