This document covers several theorems regarding similar triangles: AAA, AA, and SAS similarity theorems state that if corresponding angles or sides are proportional, the triangles are similar. The SSS and L-L theorems for right triangles also make claims of similarity based on proportional sides. Examples demonstrate applying these theorems to determine if triangles are similar and to find missing side lengths. The proportional segments theorem is also described as relating ratios of line segments cut by parallel lines.