The International Screening Network met in Rotterdam, Netherlands this year and has been gathering regularly since the late 1980s. It was started by Sam Shapiro, the father of cancer screening. He developed and ran the Health Insurance Plan (HIP) randomized trial that created the evidence used to argue for and about mammography for 40 years. Pretty important data. He thought we could merge breast cancer data from organized programs across Europe and the US. I attended my first meeting with him 20 years ago in Florence where we realized that merging data was not happening quickly. We could, however, identify common questions, and 20 years later a group of 20 people has grown into a more than 200 researchers whose collaboration has directly resulted in nearly 500 publications. The meeting this year included workshops on overdiagnosis, primary care's role in cancer screening, and building a test set of mammograms to compare the interpretive abilities of European and US radiologists, in addition to two days of lectures. The Europeans noted that the ICSN has influenced the questions they asked and the programs they ran, in part because it was the only time that so many screening scientists from countries with organized programs gathered in one place.