Client information systems (CISs) are essential tools for social care professionals: the systems should support their routine work and information management. Further, the systems are expected to be of high quality as usability of CIS is even mentioned in the national eHealth and eWelfare strategy. In the social care, it is essential to get a comprehensive view of the client’s life situation. This thesis examines the user experiences of social care professionals with the CISs they use. Specifically, the focus is on professionals' experiences of system usability in everyday tasks and how the systems support tasks crucial to their work, such as understanding the client´s individual situation. The empirical data for the study consists of a subset of the STePS 3.0 national survey conducted in 2020 among professionals with polytechnic or university degree in the field of social care. The data comprised 980 respondents and was analyzed using statistical methods. In addition, a scoping study was conducted to find out what research has revealed about the usability and user experiences of CISs in previous studies. The results indicate that 38% of the respondents rated the usability of the systems as good. Previous research also indicates that improvements in usability are needed, although there is limited international research that focuses on usability in social care customer information systems. The scoping study showed that professionals' needs for performing their work with the support of the system are in conflict with the needs of the organization. Professionals experienced that the information quality in the systems is good, but the way the information is presented in the systems does not adequately support professionals in comprehending the overall situation of the client. Usability is the strongest predictive factor for the support professionals perceive from the customer information system in forming case-based knowledge, followed by the quality of information as the second strongest predictive factor. Of the respondents, 42% felt that the customer information systems they used provided weak support, and 34% felt it provided strong support in comprehending case-based knowledge. Further research on the usability and support for forming case-based knowledge for the client is needed to utilize this research as support for the development of information systems.