Based on the author indices over the past ten years in three international journals of physics teaching, we have constructed networks of physics educators. The latter are connected if they have published one or more articles together in any one of the three journals. We obtained some important sociological characteristics of the research collaborations or linkages between physics teachers. These results indicate how experiences, ideas, and methods are shared, the degree of collaboration, the existence of clusters between physics teachers, and the productivity distribution. Many aspects of our results differ significantly from those recently found by other researchers on the co-authorship networks of scientists in various fields. The present work can serve as an example of the application of the concepts and features of social network analysis. Copyright © 2005 American Association of Physics Teachers.