The Small Animal Imaging Shared Resource (SAISR) at Simmons Comprehensive Cancer Center (SCCC) is a comprehensive small animal multimodality imaging resource that facilitates advances in the understanding of cancer biology and the development of novel therapeutics. The SAISR enables noninvasive assessment of tumor development, progression, and response to therapy based on multiple imaging technologies, including optical, ultrasound, photoacoustics, MRI, CT, SPECT, and PET/CT. In addition to anatomical visualization, the SAISR provides spatial and functional context for prognostic biomarkers and theranostic interventions. Under the leadership of Ralph P. Mason, PhD, the SAISR facilitates and integrates pathophysiology, metabolism, and receptor target identification with anatomical imaging. The SAISR provides SCCC investigators with assisted and unassisted usage of imaging technologies, consultations on optimal imaging approaches, and hands-on training in the use of imaging modalities. Since the last renewal, the SAISR has incorporated several new approaches in order to stay at the leading edge of technology. Important enhancements in infrastructure and capabilities include new photoacoustic tomography and access to short-lived isotopes generated by a new cyclotron that provides multiple tracers, including 18F-MISO, 11C-acetate, and choline, that can be observed with a new Mediso PET/CT scanner. There have also been substantial upgrades to the MRI facilities that significantly expand the new preclinical radiation services so that investigators can use MRI and image-guided irradiation inside a specific pathogen-free vivarium, complementing the existing instruments in conventional animal housing areas. These capabilities of the SAISR were utilized by 41 investigators across four SCCC research programs in 2019 and provided key data and insights to support the success of more than 30 peer-reviewed, funded research project grants and 119 peer-reviewed publications since 2014, including work published in high-impact journals such as Nature, Nature Communications, Nature Neurosciences, Journal of Clinical Investigation, Gastroenterology, and the Journal of the American Chemical Society. In summary, the SAISR advances, supports, and provides important cancer research imaging modalities to the SCCC community, enabling them to efficiently test new therapeutic strategies in vivo as well as facilitate companion studies in clinical trials.