Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Encyclopedia of Triangle Centers (ETC) is an on-line list of more than 3,000 points or "centers" associated with the geometry of a triangle. It is maintained by Clark Kimberling, Professor of Mathematics at the University of Evansville. Each point in the list is identified by an index number of the form X(n) for example, X(1) is the incentre. The information recorded about each point includes its trilinear and barycentric coordinates and its relation to lines joining other identified points. Links to Geometer''s Sketchpad diagrams are provided for key points. The Encyclopedia also includes a glossary of terms and definitions.