In 1978, more than 100 science educators from Israel and approximately 50 leading science educators and researchers representing 13 countries convened at the Weizmann Institute of Science, Rehovot (23-28 July) and The Hebrew University, Jerusalem (30 July-2 August) to discuss problems and issues of curriculum development and curriculum implementation in science. Forty years ago, when the revolutionary reform in science education emerged, many of these issues were new. Before that time, curricula had been developed locally, by those who planned to teach them; as a consequence, terms like dissemination, diffusion, utilization, and implementation were rarely used. The importance of such terms became evident as the movement of curriculum development at the national level gained prominence, especially in science. Today, drawing on the experiences of the last 30 years, we are not only able to specify what curriculum developers have to consider in terms of implementation, but we can also draw some significant conclusions from our experiences with implementation for curriculum development in the future. The most important general conclusion is that curriculum development and implementation should not be viewed as two separate processes, but rather as one interactive process. The purpose of this paper is to describe the nature of this interaction and the factors which may influence it.