Although the information-seeking behavior of postgraduate students has of recently started to attract the attention of international scholars, there is still a lack of such studies in the field of information science both internationally and in Croatia. As writing a doctoral dissertation is a long and demanding process, and information-seeking is an essential part of this process, the goals of this research are to find out: (RQ 1) how do doctoral students obtain the information they need for writing their doctoral dissertation, (RQ 2) how do they decide which information sources to use, (RQ 3) what difficulties do they encounter during information-seeking and information use, (RQ 4) what form of help do they need to overcome difficulties during information-seeking and information use, and when do they need such help, and (RQ 5) which factors (demographic characteristics) influence their information behavior. This research employs Kuhlthau's model of the Information Search Process (ISP), used for the identification of physical (actions), cognitive (thoughts), and affective (feelings) dimensions that influence the information-seeking behavior of postgraduate students. As the centre of ISP model is the principle of uncertainty, from which the concept of zones of interventions has been developed, this research also tries to understand in what way supervisors and librarians can help postgraduate students in the complex research process, regarded as crucial for writing a doctoral thesis, with the ultimate goal of proposing possible zones of intervention as a form of support for this user group. This research was conducted in two phases. A pragmatic approach and explanatory sequential strategy, including quantitative and qualitative research methods, were used. The research sample consists of postgraduate students from the field of social sciences and humanities in the Republic of Croatia. Characteristics of the respondents included those: who defended their doctoral thesis within the last year, who were in the process of waiting for the doctoral thesis defence, who submitted the completed doctoral thesis to a supervisor (cosupervisor) for reading, or those who have written a major part of their doctoral thesis. The research sample for the questionnaire consisted of 194 postgraduate students from the social sciences and humanities field, and the sample for semi-structured interviews consisted of 16 respondents. The research was conducted between April and July 2022. The first quantitative research phase included a questionnaire method and aimed to answer three research questions (RQ 1 How do doctoral students obtain the information they need for writing their doctoral dissertation?, RQ 2 How do they decide which information sources to use for writing the doctoral dissertation? and RQ5 Which factors (demographic characteristics) influence their information behaviour?), and to determine the patterns of the their informationseeking behavior. The results of the quantitative research were used to develop interview guide. In the second, qualitative research phase, the topics are further investigated to gain a deeper insight into the research problem. The findings obtained in these two research methods provide a basis for a thorough understanding of the research problem. The findings show that postgraduate students most often use relevant information in electronic form and most often find it by searching full-text databases and the Internet search engines such as Google and Google Scholar. Postgraduate students most often decide to use free available sources, i.e. open-access sources and those they frequently use. They encounter many difficulties during information-seeking and information use, such as the lack of time which prevents them from work regularly and continuously on their thesis. However, they also mention difficulties in access to relevant scientific information (e.g. subscriptions to online databases) and a lack of skills in using specific technologies. Although the majority of the respondents used the library when searching and using relevant information, they do not turn to librarians for help on regular basis. Also, the results showed that help from the supervisor is needed in all phases of informationseeking and the use of relevant information, which confirms that the supervisor has an essential role in postgraduate education. Besides librarians and supervisors, postgraduate students sometimes sought help from other teachers, relevant authors, domestic and foreign scholars and their peers. The choice of persons they turn to for help differs for every respondent. Most respondents need help when searching for information required to write their doctoral thesis. Respondents believe that they would benefit from the cooperation of supervisors with other postgraduate study professors and librarians. Since postgraduate students are not a homogenous group, it is essential that a librarian can determine which difficulty postgraduate students encounter and when so that they can determine which type of intervention will help them in the specific phase of the information-seeking process. Concerning different demographic characteristics, the research findings show that different factors influence the information-seeking behavior of postgraduate students. Among the most important ones are scientific field and work experience. Also, the results showed that postgraduate students' information-seeking is accompanied by a range of feelings, from negative ones in the early phases to a sense of satisfaction at the end of the information-seeking process. This research contributes to a better understanding of the information-seeking behavior of postgraduate students. It deepens scientific knowledge about the influence and importance of different forms of help on the information-seeking behavior of postgraduate students during their postgraduate studies and especially during the process of writing the doctoral thesis. It also highlights an important user group that has been insufficiently explored, especially in Croatia. This research also contributes to the development of scientific methodology and future research agenda (research questions to be asked in future studies).