The intent of this paper is to probe the application of web 2.0 in selected libraries in Delhi and awareness of web 2.0 technologies by library professionals. The main focus on the research was to be aware of web 2.o tools and its use by libraries in providing better services and enhances learning process to users. A questionnaire was framed and used for collection of data from library professionals from selected libraries in Delhi. The study reflects the familiarity and awareness of library professionals with web 2.0 tools such as blogs, wikis, Facebook, twitter, Instant messaging etc. The study revealed most frequent purpose of using web 2.0 tools was reference service, training, blogging, announcements, OPAC, new arrivals and sharing purpose with users. There was some of the challenges faced by library professionals in using web 2.0 tools such as power failure, slow internet, lack of skills etc.