Multiarch is a fundamentally simple idea that extends the basic lib / lib64 idea to allow arbitrary architecture combinations. This co-installability of software of different ABIs and architectures, has obvious applications in emulation, cross-building, legacy binaries and cross-grading. It has been initially implemented in the Debian ecosystem, and may never make it to RPMworld, but it's an important concept that nevertheless deserves wider understanding across distros. Having used it for a couple of years I have been impressed at how useful it is, and find the orthogonality of the design very pleasing. This talk will explain how it works and show how it's used, but also use it as an example in the wider context of making big and disruptive changes like this in the ecosystem, reviewing what went well and what didn't. https://wiki.debian.org/Multiarch