Series Type Interpretations Interpretation/Approach Riso and Hudson introduced additional concepts to the types including levels of development, integration/disintegration, and various triads. Related Links The Enneagram Institute The Enneagram Institute YouTube Channel The Nine Types In Brief - The Enneagram Institute Related Books and Media Related Videos Enneagram Type 1 by Russ Hudson Enneagram Type 2 by Russ Hudson Enneagram Type 3 by Russ Hudson Enneagram Type 4 by Russ Hudson Enneagram Type 5 by Russ Hudson Enneagram Type 6 by Russ Hudson Enneagram Type 7 by Russ Hudson Enneagram Type 8 by Russ Hudson Enneagram Type 9 by Russ Hudson , Interviews with Russ Hudson