Two studies on students' conceptions/notions about the energy concept are presented. The first (study A) dealt with learning the energy concept during a grades 7/8 instructional unit ("energy, work, force, and power"). The second (study B), using students in West Germany, Switzerland, and the Philippines as subjects, examined outcomes of physics instruction in grades 6 and 10 with regard to the energy concept. A two-part questionnaire (included in an appendix along with questionnaire evaluation categories) was used before and after instruction in both studies. The first part focused on the meaning of the words (concept names) energy, work, power, and force. The second part focused on application of the principle of energy conservation in simple mechanics' processes. In addition, some students were interviewed to clarify their responses (before and after instruction). Among the detailed results reported are findings that physics instruction does not alter drastically students' notions about energy. In addition, most students preferred conceptions and notions stemming from everyday experiences. This suggests that energy should not be restricted to the ability to do work, that the traditional way to energy concept via work causes severe learning difficulties, and that energy conservation/degradation should be given more instructional emphasis. (JN)