This proposal is a competing renewal application for continuing support of a T32 training grant entitled “Virus- host interactions: a multi-scale training program.” The program, formerly called Molecular Biology of Eukaryotic Viruses, was established at the University of California, Irvine (UCI) in 1988. During its 30-year history, the goal of this program has been to broadly train Ph.D. graduate students in the fundamental aspects of molecular and cellular virology as they relate to virus-host interactions, viral pathogenesis, regulation of viral gene expression, virus structure/proteomics, and applications of virus/phage technologies. During the current review period (9/14-8/19), eight predoctoral students were supported by this training program. For the upcoming budget period, three pre-doctoral trainee positions are requested, consistent with previous renewals of this program. Due to evolving faculty research expertise and the emergence of new virus/phage- related disciplines, the scope of proposed training areas will be broadened to also include interdisciplinary research and training programs in host responses to viral infections, bacteriophages in the human microbiome and the environment, and mathematical modeling of virus dynamics. There are 13 faculty mentors for this program, representing eight academic departments at UCI. Nearly all faculty members from these departments participate in the Cellular and Molecular Biosciences graduate program (CMB) at UCI, which oversees recruitment, admission, and first-year training of predoctoral students. The majority of the T32 training grant trainees are part of the Immunology and Microbiology focus area in the CMB program. Three of the training preceptors are affiliated with the Department of Ecology & Evolutionary Biology, and research in these labs will focus on (i) viruses/bacteriophages in the environment, (ii) viruses associated with the human microbiome, and (iii) in vivo virus dynamics. All trainees in the proposed training program will take formal course work that includes an integrated set of core courses in molecular virology/pathogenesis, phage-host interactions, mathematical modeling of virus spread, and a Virology Journal Club as well as electives and seminar courses in their areas of research specialization. The virology training faculty have major research strengths in virus-host interactions including the immune response to viral infections, regulation of viral gene expression, structural virology and viral proteomics, viral pathogenesis, control of emerging virus infections, viruses/bacteriophages in the human and environmental microbiome, modeling of virus populations, molecular evolution of viruses, virus gene therapy, and drug delivery via viral vectors. Our research programs cover a wide range of DNA and RNA viruses, including herpes simplex virus, varicella zoster virus, vaccinia virus, adeno-associated virus, bacteriophages, retroviruses (HIV), filoviruses, arenaviruses, fla...