This case study describes the peer evaluation system the Maricopa County Educational Services Agency (MCESA) is using in the districts participating in its Teacher Incentive Fund (TIF) 3 and 4 grants. Maricopa County's TIF districts cover much of the Phoenix, Arizona, metropolitan area. Including both TIF 3 and 4 cohorts, 12 districts with a total of 82 schools are participating in the TIF project. This brief first discusses the potential advantages and challenges of implementing peer evaluation and then describes the design and evolution of MCESA's peer evaluation process and what is currently known about its impact on teachers and school leaders. The results of teacher evaluation results indicate that the peer evaluation process results in a more symmetric distribution of teacher effectiveness many have expected more rigorous evaluation systems to yield. The article concludes by presenting the lessons MCESA learned in operating the peer evaluation program since the 2012-13 school year.