Ultrathick sectioning can in principle be used to reduce even very large blocks of embedded tissue (perhaps even an entire mouse brain) to sub-blocks optimally-sized for re-sectioning and imaging by any of today's connectomics technologies. Ultrathick sections cut along one plane through the tissue are re-embedded with blank spacers and cut in an orthogonal plane (see Figure 1i for example). Repeating this reduces the original volume to slabs filled with cubes of tissue separated from each other by blank resin. Individual cubes can be extracted for imaging in any order desired, creating a random-access “library” of tissue samples. Besides optimizing sample size and allowing parallel imaging across multiple technologies, such a library would also allow more precise targeting of imaging resources within a larger tissue volume. This would allow for follow-up studies to extend a connectome imaged and traced in one region into neighboring regions.