This study aims to identify what curriculum resources preservice teachers are using when planning a lesson individually and with a group. Moreover, it is interested in understanding the criteria they use when selecting curriculum resources in their lesson plans. The data were obtained from 28 preservice mathematics teachers through a written questionnaire, individual lesson plans, group lesson plans, and focus group interviews in a period of nine weeks. In the individual lesson planning process, most of the preservice teachers used both the activities from the prescribed textbook and ready-to-use internet-based resources. They included one type of curriculum resource in a phase of individual lesson plans. However, some groups used multiple curriculum resources in a phase of the group lesson plans. The groups produced a shared understanding of the selection of curriculum resources and produced a joint lesson plan by reviewing their choices in individual lesson plans. In both individual and group lesson planning, the frequency and types of curriculum resources used in the lesson plans notably varied according to the mathematics contents and the phases of the 5E (Engage, Explore, Explain, Elaborate, Evaluate) lesson plans. When selecting curriculum resources, preservice teachers considered learner-related, teaching-related, mathematics-related, and constraints-related criteria.