SUMMARY Cell division, cell signaling and trafficking involve exquisitely sensitive, dynamic molecular interactions, often at the level of single molecules. Investigating these processes, especially in live cells, requires visualization of structure and dynamics below the diffraction limit of visible light. Previously, this resolution was only achieved in fixed, highly processed samples visualized in the electron microscope. However, recent advances in optics and image processing have made an investigation of dynamic high-resolution structures possible in the light microscope. The highest resolution are afforded by the structured illumination microscopes which illuminate samples with a grid pattern at 3-4 angles and reconstruct the image computationally.To be practical for live imaging, high speed and sensitivity are essential. At this time the highest resolution combined with the fastest speed is provided by the DeltaVision? OMX Blaze 3D structured illumination microscope (SIM). We are requesting this instrument for the investigation of a number of collaborative, interdisciplinary projects at the University of Washington. The Wordeman and Asbury labs will investigate the dynamics of the kinetochore-microtubule interface determine the fidelity of chromosome segregation during cell division. High-resolution imaging will enable, for the first time, microtubule nucleation by centrosomal components to be quantified with confidence (Wordeman, Davis, Kollman and Cabernard labs). This instrument is required for high-resolution imaging of vesicle and synaptic vesicle trafficking and signaling complexes (Merz, Hoppins, Ailion and Paredez labs) and also of actin dynamics during growth of the pathogen Giardia intestinalis (Paredez lab). Signaling complexes and interacting regulators can be probed with high spatial and temporal resolution by the Hille, Koh, and Froehner labs. Finally, projects studying fertilization and oogenesis in Drosophila (Wakimoto lab) and the regulation of photorespiration in plants (Torii) will benefit from super resolution imaging.