Internet of Things (IoT) is one of the revolutionary technologies brought by the 4th Industrial Revolution that will enable a shift from a virtual object network to a virtual network of physical things. That means that physical things will become “smart” by being connected to the internet which will result in a new generation of mobile and web services. Smart things, devices, and infrastructure will, at one point, become Smart Cities, Smart Institutions and Smart Industries. Thus, the library which is implementing these technologies will become a Smart Library. In librarianship, the concept of is being mentioned in literature since the 2000s. The term is increasingly used to define new models for effective technology integration for evolving the library services, and in the minor part of the literature it is associated with the use of Smart technologies in the construction and equipping of the library building. Project Smart Library NSK - Prototype of IoT Technology in Libraries is the first such project in Croatian libraries. The aim of the project is to explore the possibilities of using IoT technology in the library environment by creating a mobile application prototype that will serve as a Smart Guide based on beacons in the physical space of the National and University Library in Zagreb. Its main aim is to virtually connect users and the Library, both in terms of space and services. Some of the IoT possibilities for the library environment include user profiling, micro-location targeting and indoor navigation, creation of dynamic content and actions based on individual user behavior, pattern analysis and user behavior, personalization and on-demand service delivery, contextualization of space and materials, edutainment in the form of interactive quizzes or treasure hunts enriched with extended and virtual reality. Through partnering with the University the project aims to develop an open source solution that other institutions can adopt and adapt to its needs. Project activities include exploration of user needs by means of creating user personas and scenarios, installation of the physical beacon infrastructure, development of backend system and mobile application design and development, system testing and utilization research, dissemination of research results, maintenance and planning of further developments. Undoubtedly, the library has to go where its users are, and they are increasingly turning to digital services and content in meeting their information needs. Users expect the content to come to them, when they need them and where they want it, preferably fast, personalized and tailored to their specific requirements. The long-term vision of the National and University Library in Zagreb is to improve the position of libraries in Croatia in a fast developing new digital era and to foster their transformation into a contemporary space while promoting the development of digital technologies and their application in society through the widespread use of innovative products and services. Research and application of these technologies will enable libraries to seamlessly connect with the digital infrastructure of the future while being in full control of the platforms and systems behind them.