Issues regarding scientific explanation have been of interest to philosophers from Pre-Socratic times. The notion of scientific explanation is of interest not only to philosophers, but also to science educators as is clearly evident in the emphasis given to K-12 students' construction of explanations in current national science education reform efforts. Nonetheless, there is a dearth of research on conceptualizing explanation in science education. Using a philosophically guided framework--the Nature of Scientific Explanation (NOSE) framework--the study aims to elucidate and compare college freshmen science students', secondary science teachers', and practicing scientists' scientific explanations and their views of scientific explanations. In particular, this study aims to: (1) analyze students', teachers', and scientists' scientific explanations; (2) explore the nuances about how freshman students, science teachers, and practicing scientists construct explanations; and (3) elucidate the criteria that participants use in analyzing scientific explanations. In two separate interviews, participants first constructed explanations of everyday scientific phenomena and then provided feedback on the explanations constructed by other participants. Major findings showed that, when analyzed using NOSE framework, participant scientists did significantly "better" than teachers and students. Our analysis revealed that scientists, teachers, and students share a lot of similarities in how they construct their explanations in science. However, they differ in some key dimensions. The present study highlighted the need articulated by many researchers in science education to understand additional aspects specific to scientific explanation. The present findings provide an initial analytical framework for examining students' and science teachers' scientific explanations.