<p>During transition planning for individuals with intellectual and developmental disabilities (IDD), family-school partnerships are critical for post-high school success. Siblings of individuals with IDD fulfill essential roles within a family unit and may fulfill caregiving responsibilities as their brothers and sisters with IDD transition into post-high school settings. Despite their important roles, siblings are often not included in transition planning. Thus, it is critical to understand sibling perspectives and roles in transition planning. To this end, 10 siblings of individuals with IDD participated in individual interviews about transition planning. Siblings reported family, school, accessibility, and systemic barriers to their involvement in transition planning. Further, siblings reported support needs with respect to: their roles, relationships, finances, and available services. Implications for research and practice are discussed.</p>