Today public libraries act as urban catalysts for the promotion of cultural policies, and may represent significant nerve centres not only within the whole cultural system, but also within the welfare system of a city. But if a library is to be successful, the building's architecture and the spaces and furnishings contained in it are just as important as the services offered. So the main purpose of this paper is to propose guidelines and examples for planning and designing public libraries, and to illustrate features and requirements not only from the architectural point of view but also from technical-functional one, with special regards to the activities, the uses and the needs of the library program. A new model of public library is presented, intended for the Italian present situation, and some Italian projects are described, trying to find some keywords for the design of cultural spaces in the city of the future.