Apptainer is a secure container technology designed to be used on for high performance compute clusters. This workshop will focus on how to use Apptainer as well as how to make use of tools such as Conda and Spack within Apptainer. By the end of these sessions, one: will have learnt about Apptainer and how it is installed and used on our computer clusters, how to build an Apptainer container image, how to install tools such as Conda/Spack from inside an Apptainer container shell, and, how to use Apptainer containers within job submission scripts. Level: Introductory Length: Two 3-Hour Sessions Format: Lecture + Hands-on Prerequisites: Experience using Alliance compute clusters, e.g., using the BASH shell and submitting jobs. (part of the 2024 Compute Ontario Summer School)