The diary has long served as a meaningful tool for psychological transformation. This article examines diary writing as a dynamic space for emotional expression, reflective thinking, and narrative construction. Through a narrative review of peer-reviewed literature, primarily focused on publications from 2010 to 2025, and supplemented by foundational earlier studies, this paper explores the psychological functions of diary and journal writing across domains such as education, mental health, and personal development. Special attention is given to how writing facilitates self-awareness, emotional regulation, and identity construction. A structured search strategy was employed across five databases – Scopus, Web of Science, PsycINFO, PubMed, and ERIC – yielding a curated set of 15 empirical studies relevant to the intersection of journaling and personal transformation. These studies were analyzed thematically and grouped into five domains: (1) self-reflection and cognitive integration; (2) emotional regulation and psychological containment; (3) meaning-making in times of disruption; (4) identity formation and personal development; and (5) educational and professional applications. Findings indicate that diary writing is not merely a retrospective activity but a transformative narrative practice, through which individuals externalize experience, process emotion, and shape evolving self-concepts. The integrative function of writing is thus positioned as both a psychological intervention and a personal method for engaging with change.