The decision by public libraries in New Zealand to implement Facebook has been uneven. Using Rogers' Diffusion of Innovations theory, a survey of nine public libraries investigated the process of its adoption or non-adoption. The motivating factors for the adoption of Facebook were identified. The surveyed libraries all met the four prior conditions for its adoption. In the innovation-decision process libraries fulfilled the knowledge stage to differing degrees. In the persuasion stage the attributes of relative advantage, compatibility and complexity were the most important factors to explain adoption. Other factors favouring adoption, such as the importance of change agents, were also discovered.