3VIL is a library of utilities for the numerical evaluation of 3-loop vacuum basis integrals. It implements analytical results where known, and otherwise evaluate the basis integrals using Runge-Kutta integration of the coupled differential equations involving derivatives of the squared mass arguments. The code is written in C, and may be linked from C or C++. 3VIL is free software, released under the GPL. The authors are Stephen P. Martin and David G. Robertson. The paper announcing 3VIL, and containing the calculations on which it is based, is available from the arXiv.org preprint archive as 1610.07720. The source code for the current version (v2.01, June 18, 2020) of the program can be downloaded here as a gzipped tar file: 3vil-v2.01.tar.gz. This unpacks into a single directory, which contains the C source files and a README.txt file with complete instructions for building and using 3VIL. Note that v2.0 involves a significant update and some restructuring compared to v1.0. For more information, see the README.txt and CHANGELOG.txt files. An archive of older versions is available here. This page is mirrored here. This material is based upon work supported by the National Science Foundation under grants PHY-1417028 and PHY-1719273. The work of DGR was supported in part by a grant from the Ohio Supercomputer Center. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.