To many, the contents of this conference may not seem appropriate at a time when the minds are preoccupied with a "population explosion." To the participants and guests of this conference, however, this was a week of fascinating discussions. While quantitative aspects of reproduc tion were touched upon, it was mostly a search for an understanding of the qualitative aspects of reproduction and its failure. Only when we understand these more completely will it be possible to render optimum care and have the foundations for meaningful population control. The conference was conceived in discussions at the Committee on Pathology of the National Academy of Sciences, W"ashington, in 1965. It was felt that investigators in medicine and the veterinary fields would profit greatly from a closer liaison. All too frequently, we work relatively isolated in our respective fields and, with the burgeoning information filling our journals, we have not enough time and leisure to stand back and attempt a comparative look at the subject of study. Often we are not familiar with the techniques other disciplines use, and which we could well employ to great advantage. ,,yhile this applies to many aspects of medicine, a comparative approach to the study of reproductive failure seemed most advantageous at this time.