Objective - The aim of this study was to evaluate Integrated Library System (ILS) use in university libraries in Nigeria in terms of their adoption, performance, achievements, and shortcomings and to propose a rigorous model for ongoing evaluation based on use of candidate variables (CVs) derived from the approach used by Hamilton and Chervany (1981) and from evaluation criteria suggested by Farajpahlou (1999, 2002). Methods - The study adopted a descriptive survey design. Nigeria is made up of six geo-political zones including: North-East (NE), North-West (NW), North-Central (NC), South-South (SS), South-East (SE), and South-West (SW). The population for this study comprised Systems/IT and E-librarians in the university libraries from all six of the geo-political zones of Nigeria. Because of the large number of universities in each of the zones in Nigeria, a convenience sampling method was used to select six universities representing federal, state, and private institutions from each of the six geo-political zones of Nigeria. A purposive sampling method was used to select the Systems/IT and E-librarians who were directly in charge of ILS in their various libraries. Therefore, the sample for this study was made up of 36 Systems/IT and E-librarians from the 36 selected universities in Nigeria. The instrument used to elicit responses from the respondents was an online questionnaire and was distributed through the respondents’ email boxes and WhatsApp. The questionnaire administration received a 100% response rate. Results - Findings revealed that university libraries in Nigeria have made remarkable progress in the adoption and use of ILS for library services. The findings also showed that much has been achieved in the use of ILS in library services. Evidence in the study indicated that the performance of the ILS adopted in the selected university libraries in the area of data entry and currency, accuracy, reliability, completeness, flexibility, ease of use, and timeliness was encouraging. Conclusions - Adoption and use of ILS in libraries is changing the way libraries deliver services to their patrons. Traditional methods of service delivery are different from the expectations of the 21st century library patrons. The transformation seen in the university libraries in Nigeria using ILS was tremendous and is changing the narratives of the past. However, several shortcomings still exist in the adoption and use of ILS in university libraries in Nigeria. Overcoming some of the limitations would require a conscious effort and decisiveness to ensure that librarians and library patrons enjoy the best services that ILS can offer. ILS developers should consider the dynamic needs of libraries and their patrons and incorporate specific candidate variables (CVs) in their ILS designs to enhance the quality of the services being offered to the library patrons.