In this article we present results from a project to develop survey measures of the content knowledge teachers need to teach elementary reading. In areas such as mathematics and science, there has been great interest in the specialized ways teachers need to know a subject to teach it to others -- often referred to as pedagogical content knowledge. However, little is known about what teachers need to know about reading to teach it effectively. We begin the article by discussing what might constitute content knowledge for teaching reading and by describing the survey items we wrote. Next, factor and scaling results are presented from a pilot study of 261 multiple-choice items with 1,542 elementary teachers. We found that content knowledge for teaching reading included multiple dimensions, defined both by topic and by how teachers use knowledge in teaching practice. Items within these constructs formed reliable scales.