The doctoral thesis entitled Family names in Varaždin – overview of the change of family names system and onomastic analysis is an interdisciplinary approach to exploring the collected linguistic material from historical and contemporary sources. Once the material was collected, it was listed in tables. The tables contain cells with motivation and formation of surnames, classified by centuries, starting from the 16th century to the present. The classified and analysed material was studied including onomastic and sociolinguistic methods, putting it in the historical context. The introductory paragraph of the paper contains the reason and purpose of the study, the methodology of the work and given assumptions and hypotheses. After describing the sources of the research, the term “family names in Varaždin” is defined and the criteria for inclusion of family names in the research material are set. The theoretical framework gives a brief insight into the beginning of the nomination and the appearance of the family name as the youngest anthroponymical category. Next, the family name status is stated in the legal definitions in which the last name is part of the legal formula “personal name”, which is different from the onomastic analyses consisting of the three anthroponymical categories (family name, personal name and nickname). Furthermore, the law about personal name determines the circumstances in which legal entities can change the personal name and personal name and how many component the “personal name” may contain. Next, a brief overview of Varaždin history from the 12th century to the present is given, including a review of key events and historical processes. Lastly, attempts are made to explain the etymology of the name Varaždin in the works of Varaždin writers and with author's stance. In terms of adaptation and affiliation with kajkavian speech (dialect), the characteristics of kajkavian speech in family names in Varaždin are further illustrated. The first part of the work is concluded with the analysis and interpretation of noun formulas in the earliest history of the city (developed and late middle ages). The second part of the paper analyses and interprets the collected material that is the subject matter. First, the dictionary with a detailed analysis was written, then the onomastic material was set into a table that combines both motivation and formation of family names. Then, a comment of the motivation and formation analysis is given with statistics tables, graphs and maps. The obtained results were interpreted by sociolinguistic method and the historical context. From the analysis carried out in the historical context, a unique conclusion is reached. In the total corpus of 1617 family names, family names motivated by nickname and personal name are the most present (29 % each), such as Golub, Levak, Sokol, Vrabec, Vrček..., and Brlek, Ivančić, Martinčević, Petrović, Vincek etc. There are almost equally distributed family names with and without suffixes. The most progenitive among suffixes is -ić (55 % of family names is with suffixes, such as: Bunić, Kliček, Kudelić, Malečić, Prepelić, Rožić...). We have got several subgroups of family names motivated by nickname, and they are testifyng to a greater association and connection of our ancestors with everyday life, plant and animal world, such as animals (type Medvedec), characteristics (type Divjak) or mental abilities (type Bistrović), parts of the human body (type Prstec), those motivated by household items and food (type Ožeg, Sladović), etc. Considering the time of the city's formation and the raise of the community that gained the privilege of being a free royal city (in year 1209), based on the intersection of trade routes and trade of goods, this urban community itself attracted foreigners, offering them security, and prosperity of developed urban area. Foreigners, mostly Hungarians and Germans, brought their culture and legacy, but were assimilated by domestic Croats. For a stranger to have been accepted among the full-fledged Varaždin citizens (civis) and enjoy all the rights, he would have to go through the particular process of of becoming full rights citizen of Varaždin. At the end a few conclusions have been made: in the oldest list of Varaždin inhabitants (1520) it is already obvious that the family names are largely set; family names in Varaždin fit perfectly in the image of the Croatian family names system; the majority of today's family names of Varaždin citizens can be traced back to the 18th century, which is related to the progress of the city during the time of Maria Theresa (Varaždin is the seat of the Croatian Royal Council in 1767 – 1776) and the decree of King Joseph II on Obligatory Family Name in 1780. From 77 family names that are continuously appearing in the Varaždin (16th – 20th century), 41 of them can be classified in the term described as native family names in Varaždin (Biškup, Bregović, Brlek, Cafuk, Flajšman, Golub, Golubić, Herceg, Horvat, Horvatić, Hrženjak, Ivančić, Kolar, Kolarić, Koren, Kos, Koščak, Kovač, Kovačić, Kranjčić, Kranjec, Križanec, Lacković, Leskovar, Lončarić, Martinčević, Međimurec, Novak, Novoselec, Plantak, Posavec, Ribić, Sokol, Šantek, Šestak, Turković, Vincek, Vrbanec, Vrček, Zadravec i Zagorec). Most of the analysed family names were provided with description of motivation and were presented in the formation structure, but some of them (due to the time gap and probable changes of the record over time) remain mystery inviting on further inquiry.