This thesis examines linkages between transit extensions and displacement through gentrification and explores Somerville's readiness to address displacement associated with a proposed transit extension. Somerville, Massachusetts, experienced economic growth and gentrification following the 1984 Red Line transit extension to Davis Square and now is anticipating a Green Line extension. This study includes a review of gentrification literature, a case study of planning for Davis Square in Somerville prior to the Red Line extension, and recent interviews with practitioners from the Somerville community in the areas of affordable housing, transportation, and planning to identify measures being taken to prevent displacement associated with the proposed Green Line extension. Displacement prevention measures are being implemented in Somerville, suggesting that lessons learned from the 1984 transit extension are being applied, within the limits of political feasibility and available funding.