Personal boundaries are foundational to psychological well-being, influencing emotional regulation, self-esteem, and interpersonal relationships. This theoretical paper explores the role of boundaries in mental health, drawing from key psychological theories such as Attachment Theory, Self-Determination Theory, and Cognitive-Behavioural Theory. This discourse explores the various types and levels of boundaries, as well as how they function within families, the workplace, romantic relationships and friendships. Additionally, the theoretical review examines the role of boundaries in promoting psychological well-being, the consequences of avoiding boundary-setting, practical steps for establishing and maintaining boundaries, and common reactions individuals may encounter when asserting their boundaries.