This paper discusses the Tiantai-understanding of ”interpenetrative coherence of the Dharmadhātu,” particularly that of Zhiyi and Zhili. ”Interpenetrative coherence of the Dharmadhātu” is the basic doctrine of the ”Avatamsaka Sūtra” and also the basic thought of Tiantai-Buddhism. First, I will explain the doctrines ”three thousand dharmas in one thought-moment” and ”threefold contemplation in one mind” viewed from the meaning of ”interpenetrative coherence of the Dharmadhātu.” Then, I will further discuss Zhili's explanation of the ”interpenetrative coherence of the Dharmadhātu.” This includes the ”inconceivable substance of Dharmadhātu,” ”three thousand dharmas in one thought-moment,” ”paramārtha-satya or supreme truth,” ”containment (or inherent entailment) of three thousand dharmas in any rūpa.”