This overview of the current state of availability of free/libre and open source software (FOSS) products, organisations and resources is intended to provide an introduction to the possibilities for health professionals and health informaticians who are interested in exploring the potential use of FOSS within their organisation, or simply for their own personal use. The initial question 'what is free/libre and open source software?' is addressed, so as to provide a basic level of information for those unfamiliar with the terms. Some of the commonly available FOSS applications for everyday use are introduced, before consideration is given to the issues that should be addressed when considering a migration to FOSS from commercial and proprietary software. Some of the many health-related FOSS applications and briefly introduced, and an overview is given of the international organisations devoted to providing an exploration of FOS for health informatics professionals, and which they can join. Due to the limited space available to discuss some of the issues, information is also provided on some of the many resources through which the reader can explore the issues in more depth.