SPIDER (System for Processing Image Data from Electron microscopy and Related fields) is an image processing system for electron microscopy. Emphasis on: Toolkit for algorithm development Averaging of single particles 3D reconstruction Multivariate data analysis Object segmentation from volumes Electron tomography. Features: Interactive command line interface. Hierarchical modular design for scripting. Graphical User Interface, Web, for visualizing and interacting with images. File format interchangeable with other scientific imaging softwares. Extensive documentation of operations and techniques. Includes executables and source code for use on Linux. History: Originated in 1978 at the Wadsworth Center in Albany, NY by Joachim Frank who shared the 2017 Nobel Prize in Chemistry for his pioneering cryo-em research done at the Wadsworth Center in Albany. Contributors (in chronological order): J. Frank, B. Shimkin, H. Dowse, D. Parsons, L. Miranda, C. Mannella, A. Verschoor, J. P. Bretaudiere, M. V. Heel, M. Radermacher, R. Banerjee, A. Leith, J. M. Carazo, P. Penczek, L. Odesanya, S. Sibal, Y. H. Li, M. Ladjadj, Y. Chen, K. R. Lata, J. Zhu, J. Su, W. P. Liu, B. Rath, C. Yang, B. Baxter, R. Hegerl, A. Frangakis, L. Joyeux, Z. Huang, R. J. Renka, T. Shaikh, J. Sengupta, J. LeBarron, N. Boisset, H. Gao, G. Kishchenko, J. M. Kennedy. Maintained by: ArDean Leith & Tanvir Shaikh. During the last 11 years they have added numerous operations, procedures, parallelizations, and over 500 pages of documentation. There have been no significant contributors other than Leith, Shaikh, Kischenko, and Kennedy since 2007.