This paper deals with market research as a tool in solving entrepreneurial ventures, more precisely about the data that are collected and then used in the process. When processing market data, two types of sources from which they are derived are defined.. Sources are a key part of this type of research, because they provide information and data on the basis of which answers to problems are obtained and on the basis of which final business decisions are made. These business decisions determine the fate of the company. Proper use of secondary data sources builds the foundations of future business decisions, and in order to "build" that decision to the end, primary data sources will be used. Sources of secondary data, such as Eurostat, the Central Bureau of Statistics and the Croatian Employment Service, are large-scale databases where it is possible to collect a variety of data which are of key importance in decision-making. The more specific the data, the better the results. During the research process, it is necessary to continuously review the correctness, authenticity and timeliness of the collected data. Whatever type of data and their source the company chooses, it should be borne in mind that making a profit is at the forefront, and there is no profit if there are no satisfied customers. Insight into the theory of secondary data, what they are and how they are used, differentiates different sources from which it is possible to collect them. Using our own databases or reviewing data collected by another company for the purposes of its research provides the secondary data needed for a particular research. A larger amount of this data is also collected by searching online databases and hiring agencies specializing in this type of work. Using the database of the Croatian Bureau of Statistics, Eurostat or the HZZZ, the researcher obtains the data necessary to solve the problem. This process achieves both time and money savings, which indicates that it is economically viable to use different sources of secondary data on the way to the realization of an entrepreneurial idea.