Lately we have seen a growing interest from both public and private organisations to adopt Open
Source Software (OSS), not only for a few, specific applications but also on a more general level
throughout the organisation. As a consequence, the organisations’ decisions on adoption of OSS are
becoming increasingly more important and complex. We present three perspectives organisations can
employ in their decisions: seeing OSS acquisition as a business case, as COTS acquisition, and as architectural
change within a governance framework. We present case studies of decisions on OSS
adoption, and categorise the decision criteria we have found. Our results indicate that for large-scale
adoption of OSS, focus will be on architectural considerations: enterprise-wide architectures will at
first be a barrier, but in the long term OSS’s support of open standards can be a major enabler for
OSS adoption. In contrast, in smaller organisations and in small-scale adoption of OSS, the cheap
price of OSS is a major enabler, as it provides a good opportunity for experiments and short-term
economic benefits. For small organisations these experiments can lead to development of a common
IT-architecture, and in larger organisations OSS can be adopted in niche-areas, without significantly
violating an existing IT-architecture.
Keywords: open source, COTS, IT architecture, governanc