In this article the author introduces a concept she calls "Thirdspace identity construction," which instructors can use to understand what happens in students' texts when such ever-open possibilities for identity exploration are allowed. This concept borrows from the work of critical geographer Edward Soja. Soja's "Thirdspace" represents a dynamic realm in which established binaries/dualisms that dominate the contemporary cultural understanding (such as subject/object, social/historical, center/margin, real/imagined, material/mental) are reworked in an effort to open up other possibilities for understanding. Soja uses Thirdspace as a lens to analyze what he calls "real-and-imagined" urban centers, such as the city of Los Angeles. As Thirdspaces, Soja shows how urban centers exist as triads of the spatial-social-historical, despite the tendency to consider them exclusively in the realm of the social-historical. The author applies the notion of Thirdspace not to urban centers, but to understanding constructions of identity in the composition classroom. Offering students the space in which to negotiate the infinite ways they are spoken--by their cultures, histories, and experiences--and the opportunity to compose new ways of speaking, engenders constructions of the self the dynamics of which one can better appreciate through the lens of Thirdspace. Thirdspace identity construction--as a way of understanding the compositions of students that take place when non-traditional approaches to identity are allowed and encouraged--can help instructors reinvision the possibilities for personal writing in the classroom and open up avenues for students to articulate real-and-imagined, spatially-situated selves that engender a new kind of agency: one that embraces complexity and refuses reduction. Further, when allowed to conceive of and create more complex possibilities for identity, students come to value the diversity of their selves and in doing so appreciate the diversity of others. (Contains 9 notes.)