Evaluation research can be defined as a type of study that uses standard social research methods for evaluative purposes, as a specific research methodology, and as an assessment process that employs special techniques unique to the evaluation of social programs. After the reasons for conducting evaluation research are discussed, the general principles and types are reviewed. Several evaluation methods are then presented, including input measurement, output/performance measurement, impact/outcomes assessment, service quality assessment, process evaluation, benchmarking, standards, quantitative methods, qualitative methods, cost analysis, organizational effectiveness, program evaluation methods, and LIS-centered methods. Other aspects of evaluation research considered are the steps of planning and conducting an evaluation study and the measurement process, including the gathering of statistics and the use of data collection techniques. The process of data analysis and the evaluation report are also given attention. It is concluded that evaluation research should be a rigorous, systematic process that involves collecting data about organizations, processes, programs, services, and/or resources. Evaluation research should enhance knowledge and decision making and lead to practical applications.