Social Penetration Theory is a psychological framework that explains how relationships develop over time through the gradual sharing of personal information. Proposed by Irwin Altman and Dalmas Taylor in 1973, the theory uses the metaphor of an onion to illustrate the layers of intimacy in interpersonal communication. As individuals engage in self-disclosure, they peel back these layers, moving from superficial topics to deeper, more personal ones. The theory identifies two key dimensions of self-disclosure: breadth and depth. Breadth refers to the range of topics discussed, while depth indicates the level of intimacy within those topics. As relationships progress, both breadth and depth typically increase, leading to stronger emotional connections and trust between individuals.