Libraries around the world are implementing a range of web technologies to improve the manner in which library services are delivered to users. The implementation of new technologies and functionalities is necessary if libraries are to remain relevant in the current information landscape. This research paper reports on an investigation of the prevalence of blogs, RSS, social networks and other Web 2.0 tools/technologies in Irish public and academic libraries, along with the purposes for which these Web 2.0 tools are used. Also, the relation between implementation of Web 2.0 tools and Library 2.0 is examined in the Irish context. A mixture of survey research and content analysis was undertaken to obtain a complete set of data for a census on Web 2.0 tool implementation in public and academic libraries. The research found that social networks are the most widely-implemented Web 2.0 tool among Irish libraries, followed by blogs and RSS technology. Other Web 2.0 tools have varying levels of prevalence. Irish librarians are of the opinion that implementing Web 2.0 tools in the library service is a major component of Library 2.0. Opinions were mixed on whether the implementation of Web 2.0 tools was motivated by a desire to achieve a Library 2.0 level of service. The research provides a current picture of the state of Web 2.0 presence in modern Irish libraries, and works towards an understanding of the impact of technological developments on libraries. It is hoped that the research will be of interest to librarians and other information professionals interested in the implementation of Web 2.0 tools in the library setting. Author keywords: Web 2.0, academic libraries, public libraries.