Urban teacher residencies (UTRs) have emerged as an innovative alternative to recruiting and preparing high quality teachers for traditionally underserved, urban schools. UTRs offer opportunities for teacher candidates and mentors to use co-teaching models to differentiate instruction, particularly as schools adopt more inclusive practices emphasizing collaboration and co-teaching among educators. Co-teaching in residencies is an area that remains largely unexplored. This study describes experiences of 37 residents and 35 mentors in three cohorts of a yearlong urban residency program as they engaged in co-teaching together in secondary math, science, and special education classrooms. Data included surveys on co-teaching and collaboration from residents and mentors, along with reflections on highlights and challenges of their co-teaching in the residency. Findings indicate that both residents and mentors had positive perceptions about the benefits of co-teaching, engaged in behaviors associated with effective co-teaching at least 1-2 times per week, and shared ideas related to communication and feedback, varied perspectives and shared ideas, benefits for students, logistics of co-teaching, sharing authority, and the motivation to do better.