Managing the distribution and installation of large and complex software suites such as that of the ATLAS Particle Physics experiment  gives rise to a variety of problems. To be able to deploy software on the Grid it must have a completely automated installation procedure that addresses issues such compatibility, updates and external software required. Installations are needed to satisfy the different requirements of the production run, a developer (with his/her own code) and the possibility to rebuild from source. A solution to this problem has been developed in the context of ATLAS software. ATLAS uses CMT  to configure and manage packages, which are the basic units of the software. Crucially for this project, CMT allows the definition and imposition of conventions for package metadata. Pacman  is a package manager that facilitates transparent fetching, installation and management of software packages. These two pieces of widely used software provide much of the functionality required to meet the packaging, distribution and installation needs of ATLAS; the main work is to interface them and solve some problems with the ATLAS software itself. To this end, additional tools have been developed to extract files in common package formats (such as tar and RPM) and write the Pacman files. These files describe all the information needed to fetch and install a package, including its dependencies on other packages. External packages are handled by additional metadata written in interface packages, thus allowing them to be packaged in a similar way. The presence of basic system packages is tested before the download and installation commences.