Dear colleagues, We would like to draw your attention to the MICCAI challenge "CREMI: Circuit Reconstruction from Electron Microscopy Images" (http://cremi.org/). As of May 1st, the training phase of the challenge has opened. We provide three volumes with dense neuron and synapse segmentation, along with annotations for pre- and post-synaptic partners (http://cremi.org/data.html). The goal of this challenge is to evaluate algorithms for automatic reconstruction of neurons and neuronal connectivity from serial section electron microscopy data. The comparison is performed not only by evaluating the quality of neuron segmentations, but also by assessing the accuracy of detecting synapses and identifying synaptic partners. The challenge is carried out on three large and diverse datasets from adult Drosophila melanogaster brain tissue, comprising neuron segmentation ground truth and annotations for synaptic connections. A successful solution would demonstrate its efficiency and generalizability, and carry great potential to reduce the time spent on manual reconstruction of neural circuits in electron microscopy volumes. Follow us on Twitter for updates (https://twitter.com/cremi_challenge) and feel free to contact us at challenge@cremi.org. Regards, The CREMI organizers (Jan Funke, Stephan Saalfeld, Davi Bock, Srini Turaga, and Eric Perlman)