Integrated Library System (ILS) switching is a very crucial project in the life of any library, and capital intensive. However, Nigerian university libraries have continued to switch ILS within a short period after deployment without reaping the cost of investment made in the first instance. This study sought to determine the reasons for switching ILS among Nigerian university libraries, the procedural and financial switching costs of ILS and factors taken into consideration while switching. Additionally, the study determined the implications of switching ILS on Nigerian university libraries. A qualitative research approach using multiple case study design was used to gain a better understanding of the problem; purposive sampling technique was used to select the participants. Interview was the instrument used for data collection, and the researcher conducted five interviews with five (5) participants from university libraries across the geo-political zones of Nigeria. Data were collected from June 2016 through July 2016. The analysis of data was done using themes derived from the objectives of the study. Findings revealed that delay in getting vendors support to fix ILS problems, some ILS have limited storage space to accommodate large data, crashing and data loss, and political considerations, were some of the reasons given by NUL for switching ILS. The study also discovered the implications for switching as delay; inability of students to use the online public access computer; time taken to populate the new ILS; and cost in terms of manpower training; while capacity to manage the system, costs, security of data, staff capacity building, hardware, power backup, services to be provided to users, availability of funding, were some of the factors considered by the libraries when switching. The study, therefore, recommended among others that Nigerian university libraries should conduct adequate and thorough feasibility study based on the peculiar needs of their libraries before selecting the appropriate library software, libraries should adopt and deploy open source ILS which are more cost effective and easier to maintain rather than buying proprietary ILS which were developed based on US and UK standards and which might not fit their needs. The study concluded that the switching over from one ILS to another by NUL studied is too frequent. The frequency of change is associated with lack of proper feasibility study and knowledge involved in determining the implications of frequent switching on the libraries.