In case library learning, an instructional method that promotes case-based problem solving, learners often struggle with indexing cases. Poor case indexing may hamper retention and retrieval of cases, hindering the construction of mental libraries in learners. To address this issue, the authors developed two indexing prompt types, explanation-based and difference-based, and explored their effects on self-explanation and problem solving in case libraries. A total of 105 students across three sections of a career development course participated in the study. Each section was assigned to one of three conditions: explanation-based indexing, difference-based indexing and no indexing prompt. Both indexing prompts facilitated self-explanation, which elaborated corresponding aspects of cases on which the prompts mainly focused. In arguing for a solution, learners relied more heavily on domain knowledge regardless of prompt types. However, both indexing prompt groups outperformed the control group in rebuttals. The authors discussed the theoretical and practical implications of the study.