Cover legend: The developmental progression of presynaptic and postsynaptic structures at a calyx of Held terminals in mouse auditory brainstem can be seen in this movie showing reconstructions of sections imaged with serial block-face scanning electron microscopy. Initially, a single cell in the medial nucleus of the trapezoid body is shown, illustrating the small size of nerve terminals contacting the cell body at postnatal day 2 (P2). Next, a P3 cell is shown with three large competing inputs (colored blue, green, and yellow in order of decreasing size) onto the cell body. The third cell is from a P4 mouse and illustrates further growth of nerve terminals and contact of the cell body by two large inputs colored blue and green. The final cell is from P6 and is dominated by a single large input enveloping the postsynaptic cell body. The P6 cell is depicted on the issue cover. For more information, see the article by Holcomb et al. (pages 12954–12969), which published in the August 7, 2013 issue. http://socofneur.http.internapcdn.net/socofneur/JN_Videos/SFN_Journal_Movie_video_2.mp4