This paper describes the implementation of an information systems infrastructure using open source software (OSS) in a large Irish public sector organization, Beaumont Hospital. The study identifies the primary organizational drivers in Beaumont’s move to OSS, namely principle and pragmatism. It also discusses some of the problems encountered, such as the change in mind-set required when deploying OSS solutions, and resistance from staff who feared being deskilled by moving away from popular proprietary systems. The study reveals a radical shift in open source deployment from invisible horizontal infrastructure systems to highly visible vertical applications. The first phase of OSS implementation is estimated to lead to cost savings of i13 million over five years. These details are useful in that few studies have quantified the savings from OSS deployment. Given that Beaumont was already receiving academic pricing discounts for many of their original proprietary closed source applications, the savings for a typical commercial organization could be even higher. Also, in many cases, the extra functionality available in the OSS systems deployed allowed for a richer feature set overall. Buoyed by the success of this first phase, Beaumont is planning a second phase of OSS implementation for an overall hospital information system, a financial systems suite, and is even considering developing their payroll system in an open source fashion. The study also identifies how a typical company can contribute back to the OSS community in their own unique way, by distributing applications developed from their own particular domain of expertise, rather than having to make code contributions to the code base of GNU/Linux or Apache as might have been assumed to be the case. Indeed, free access to source code played a very limited role in Beaumont’s motivation, where given the budgetary constraints, zero cost was of more concern than open source.