  New facilities of the 2020s, such as the High Luminosity Large Hadron
Collider (HL-LHC), will be relevant through at least the 2030s. This means that
their software efforts and those that are used to analyze their data need to
consider sustainability to enable their adaptability to new challenges,
longevity, and efficiency, over at least this period. This will help ensure
that this software will be easier to develop and maintain, that it remains
available in the future on new platforms, that it meets new needs, and that it
is as reusable as possible. This report discusses a virtual half-day workshop
on "Software Sustainability and High Energy Physics" that aimed 1) to bring
together experts from HEP as well as those from outside to share their
experiences and practices, and 2) to articulate a vision that helps the
Institute for Research and Innovation in Software for High Energy Physics
(IRIS-HEP) to create a work plan to implement elements of software
sustainability. Software sustainability practices could lead to new
collaborations, including elements of HEP software being directly used outside
the field, and, as has happened more frequently in recent years, to HEP
developers contributing to software developed outside the field rather than
reinventing it. A focus on and skills related to sustainable software will give
HEP software developers an important skill that is essential to careers in the
realm of software, inside or outside HEP. The report closes with
recommendations to improve software sustainability in HEP, aimed at the HEP
community via IRIS-HEP and the HEP Software Foundation (HSF).
