There is a growing demand for the use of renewable energy technologies to generate electricity due to concerns over climate change. The oceans provide a huge potential resource of energy. Energy extraction using marine current energy devices (MCEDs) offers a sustainable alternative to conventional sources and a predictable alternative to other renewable energy technologies. A MCED utilises the kinetic energy of the tides as opposed to the potential energy which is utilised by a tidal barrage. Over the past decade MCEDs have become an increasingly popular method of energy extraction. However, marine current energy technology is still not economically viable on a large scale due to its current stage of development. Ireland has an excellent marine current energy resource as it is an island nation and experiences excellent marine current flows. This paper reviews marine current energy devices, including a detailed up-to-date description of the current status of development. Issues such as network integration, economics, and environmental implications are addressed as well as the application and costs of MCEDs in Ireland.