This paper examines past and current experiences with fun and playfulness of participants in two summers of a National Science Foundation (NSF)-funded summer research experiences for undergraduates (REU) geosciences program. Thirty students responded to questionnaires on the role of play in their previous learning and their playful, inspirational, or "ah-ha" feelings while doing their summer research. They reported a sense of playfulness during science classes, promoted by engagement with interesting phenomena, ability to work independently, and a relaxed atmosphere. Their descriptions of playfulness in the program were similar to those of scientists describing playfulness while doing research. They described the fun of the work itself, the opportunities for playful social interactions with peers, and excitement at finding results. Implications for science education involve the inclusion of playfulness and fun in the modeling of scientific inquiry and the structuring of science classes and labs to allow more students' input into their own learning, the provision of field experiences, and the allowance of some socialization.