This paper attempts to explore the patterns of modality in selected English and Arabic self-improvement books. Self-improvement is a new genre of writing that provides readers with information and guidance on how to cope with life, resolve problems, take decisions, and achieve success. The analysis is based on Biber et al's (1999) categorization of modality. The study focuses on the use of modal verbs (i.e. can, could, will, would, shall, should, may, might, and must). It shows that different forms of modality have played an important persuasive function in the books under investigation. Prediction modality has been used to emphasize the authors' experience and comment on the positive outcomes in readers' lives as a result of applying their advice. Possibility modality has been used to present those authors' messages as a possible list of options or suggestions, not as authoritative instructions. Readers' abilities to change their inner qualities are addressed directly by the authors through using ability modality.