The Encyclopedia of Triangle Centers (ETC) is an online list of thousands of points or "centers" associated with the geometry of a triangle. It is maintained by Clark Kimberling, Professor of Mathematics at the University of Evansville.

This article relies largely or entirely on a single source. (May 2024)

As of 6 February 2024^[update], the list identifies over 61,000 triangle centers.^[1]

Each point in the list is identified by an index number of the form X(n)—for example, X(1) is the incenter. The information recorded about each point includes its trilinear and barycentric coordinates and its relation to lines joining other identified points. Links to The Geometer's Sketchpad diagrams are provided for key points. The Encyclopedia also includes a glossary of terms and definitions.

Each point in the list is assigned a unique name. In cases where no particular name arises from geometrical or historical considerations, the name of a star is used instead. For example, the 770th point in the list is named point Acamar.

The first 10 points listed in the Encyclopedia are:

Other points with entries in the Encyclopedia include:

Similar, albeit shorter, lists exist for quadri-figures (quadrilaterals and systems of four lines) and polygon geometry.

• Catalogue of Triangle Cubics
• List of triangle topics
• Triangle center
• The Secrets of Triangles
• Modern triangle geometry