During mitosis, numerous proteins accumulate around the mitotic spindle to help it assemble and segregate sister chromatids correctly. Schweizer et al. reveal that a membranous spindle envelope facilitates the accumulation of these proteins by excluding large organelles from the spindle region. This biosights episode presents the paper by Schweizer et al. from the August 31st, 2015, issue of The Journal of Cell Biology and includes an interview with the paper's senior author, Helder Maiato...