It has been five years since the instructional materials produced by the Earth Science Curriculum Project first appeared in American secondary school classrooms. An extensive search revealed that nine research studies and several surveys pertaining to ESCP have been conducted in that time. Eight of these studies and one of the surveys are reported and commented on in this review. The ninth study was in progress at this writing. Six of the studies dealt with student achievement. The findings of the six studies seem to indicate that ESCP is superior to non-ESCP earth science in affecting student outcomes. However, a clear-cut case for this could not be established. More important were the indications in two of the studies (Sargent, 1966 and Schirner, 1968) that the combination of the right curriculum with the appropriate teacher was an important factor in influencing student outcomes. Two of the studies were analyses of the content of the trial editions of Unit IV, “The Earth and the Universe.” Sonnier (1966) compared the conceptual content of college astronomy courses with the conceptual content of Unit IV. He determined that college astronomy courses provided adequate background for teachers of ESCP and that the more formal astronomy courses a teacher had in his background, the more independent he became of these courses in gaining new astronomy knowledge. Smith (1968) studied the conceptual content of Unit IV and especially Chapter 26, “The Universe and Its Origin,” in terms of its suitability for ninth graders. He concluded that the reading level and sophistication of information were both too difficult for the target audience. The one survey discussed in this review indicates that the astronomy unit was a favorite of a majority of the students who studied ESCP. The last section of the review is devoted to raising questions for further educational research. This is done through the aid of an instructional sequence model. The model depicts the major factors influencing the design of instructional procedure. These factors are shown in the paradigm as Instructional Materials and Media, Pupil Characteristics and Behaviors, Teacher Characteristics and Behaviors, Possible Instructional Means, Expected Outcomes, and Outcomes of Instruction. Questions concerning needed research appear under these headings. The Earth Science Curriculum Project has made a substantial contribution to secondary school science education in this country. Its ultimate contribution is dependent upon careful consideration and wise utilization.