Project Summary Recent methodological and technological advances have resulted in a rapid expansion of electron microscopy (EM) applications at UC Berkeley and in the wider scientific community. In particular, single particle cryo-EM applications have led to numerous high-profile advances in the field of structural biology. The equally compelling parallel fields of cryo-electron tomography (cryo-ET) and volume EM, both enabled by advances in focused ion beam (FIB) milling, have become increasingly mainstream in the study of complex biological systems. These methods allow for the direct high-resolution visualization of macromolecular and cellular structures within a native context, bridging the fields of cell biology and structural biology in an unprecedented manner. The UC Berkeley electron microscopy and cell biology communities, long at the forefront of their respective fields, have embarked upon a sustained investment in combining these promising in situ EM visualization methods. As research projects grounded in these methods have begun to mature, the need for our faculty to access cutting-edge instrumentation has become both urgent and abundantly clear. Currently, there exists no high-end cryo-capable FIB scanning electron microscope (cryo-FIB-SEM) accessible to researchers on our campus with complex, biological samples. In this proposal, we request funds to purchase a cryo-capable Zeiss Crossbeam (XB) 550 FIB-SEM and ancillary cryo-instrumentation. The cutting-edge capabilities of this instrument will greatly advance efforts at UC Berkeley to characterize biological structures across many orders of magnitude, from angstrom to millimeter length scales. The Zeiss XB 550 FIB-SEM microscope enables the determination of 3D volume-EM imaged cellular structures at both room (3 nm resolution, resin-embedded) and cryo (30 nm resolution) temperatures. With its cutting-edge capabilities in cryo-FIB milling, the Zeiss XB 550 will also be seamlessly integrated into the campus cryo-pipeline to generate cellular cryo-lamellae for later high resolution cryo-ET imaging using Berkeley’s two existing Titan Krios cryo-electron microscopes. Acquisition of the proposed system will greatly impact the work of three Major User and five Minor User groups, which are focused on important biological and biomedical questions regarding viral replication and pathogenesis, cellular signaling and nutrient uptake, oncogenesis, cilia dysfunction, and organelle biogenesis. The UC Berkeley Electron Microscopy Laboratory, expertly staffed by experienced biological microscopists who have served campus academic researchers for decades, will house the Zeiss XB 550. Our acquisition of the Zeiss XB 550 will completely modernize our EM infrastructure, accelerating UC Berkeley’s progress on a sustainable path to drive fundamental breakthroughs in cell and molecular biology.