Beginning in the mid-20th century, library automation irreversibly transformed libraries. Despite its humble beginnings when librarians were overwhelmed with work and needed help processing materials, library automation influenced the creation of MARC, online catalogs, cooperative cataloging, and eventually connected the library world globally. This thesis investigates the beginnings of automation in the United States of America. Library automation is divided into periods, each of which correlates with a specific decade of the 20th century, each with its own goals and results. In addition to the historical aspect of automation, this work deals with the consequences of computer use on librarians and users. The automation transformed the role of users in libraries in such a way that they were now expected to know how to work on a computer. They were no longer just information seekers, now they had to be able to express their queries in a computer written form. The second part of the paper deals with the automation of libraries in Croatia. The development course of automation in Croatia from the time in the SFRJ to the present is described. The key part of the work investigates the case of automation in Library of Vladimir Nazor. Automation from the very beginning is described in detail. The goal was to understand how automation took place at the level of an individual library, what were the challenges and difficulties and the consequences. Migration to another library software and functioning within the network of Libraries of the City of Zagreb were researched.