Rapidly changing technologies in libraries require continuous learning on the part of staff, particularly librarians, to keep up to date. This paper examines some of the factors affecting the participation of librarians in professional development activities. Reference librarians working in large urban public libraries in Ontario were surveyed in 2001. Data on their participation in formal and informal learning activities, together with information about their perceptions of their librariesí environment with respect to updating and learning were obtained from 553 respondents. The analysis shows that an environment which encourages learning plays a role in librariansí participation in professional development, particularly participation in informal learning activities, such as discussions with colleagues, reading and conference participation. Surprisingly, the climate for updating was found to reduce participation levels in informal activities. Having a supportive manager who provides feedback about job performance, assigns opportunities to develop and strengthen new skills and supports attempts to acquire additional training plays a positive role in the participation of reference librarians in informal professional development activities. If libraries are truly determined to become learning organizations, they must first examine their own culture of learning and climate for updating.