Empirical research regarding the impact of multimedia on learning can be traced back several decades before the large-scale invasion of multimedia learning resources (like Cd-ROM titles and Internet applications) into the educational field and originated from areas outside the educational community. Although the results are not decisive, two generations of multimedia research have contributed to establishing factors that influence effective multimedia design. We summarize the conclusions of the existing research, specifying key theoretical issues, research directions, and weaknesses associated with each generation. Emerging factors, which have begun constituting a third generation of multimedia design and learning research are discussed. Suggestions are made regarding future trends of multimedia design and learning research. (Contains 4 tables and 1 figure.)