What is the minimal information needed to say two triangles are similar?

To determine if two triangles are similar, you need to establish that their corresponding angles are equal or that their sides are in proportion. This can be done using the Angle-Angle (AA) criterion, which states that if two angles of one triangle are equal to two angles of another triangle, the triangles are similar. Alternatively, the Side-Side-Side (SSS) or Side-Angle-Side (SAS) similarity criteria can also be used if the sides are proportional.