Using common software in the LHC community

The physics application software and the corresponding infrastructure in the LHC experiments use a number of common software packages. These packages, mostly from open source projects, provide the basic building blocks and foundation on which the experiments base their specific applications and libraries, covering the areas from Monte-Carlo generators and detector simulation to trigger selection, reconstruction and physics analysis. A common effort to provide support for the common software was put in place in the Applications Area of the LHC computing Grid project (LCG AA). The spectrum of common software products presently in use will be briefly described, and some of the pros and cons of using pre-existing software in the context of HEP experiments will be discussed.