As one of the earliest extant Mahāyāna sūtra-s, Pratyutpanna-Buddha-Saṃmukhāvasthita-Samādhi-Sūtra lays foundation for “the concept of śūnya” seen in the early Mahāyāna prajñāpāramitā literature. It uniquely combines “Buddhas of the Ten Directions / Pure Land” belief and “prajñāpāramitā” theory, the two most representative systems of the early Mahāyāna thought, in the meditative practice. This thesis attempts to argue that pratyutpanna samādhi is a Mahāyāna meditative method that uses “seeing the Buddha” as the medium and puts the theory of Mahāyāna prajñā concept into practice through the Recollection of the Buddha, and the consept of “seeing the Buddha but non-cognition” penetrates the theory and pactice of pratyutpanna samādhi in order to fulfill prajñāpāramitā. This thesis points out that although pratyutpanna samādhi is a Mahāyāna meditative technique that is developed from buddhānusmṛti of the original Buddhism, its method and goal are, however, different from buddhānusmṛti. We can call pratyutpanna samādhi a paradigm shift of buddhānusmṛti in relation to the meditative practice. This thesis will also explain how Pratyutpanna-Buddha-Saṃmukhāvasthita-Samādhi-Sūtra brings forth a successful transition from śrāvaka meditation to bodhisattva meditation by skillfully interpreting the basic concepts and meditative methods of the original Buddhism in terms of Mahāyāna śūnya taught in the prajñāpāramitā literature, using aśubhāsmṛti, smṛtyupasthāna and buddhānusmṛti as examples. Pratyutpanna-Buddha-Saṃmukhāvasthita-Samādhi-Sūtra teaches about the theory and practice of śūnya, with penetration into realization as the aim of the practice. “Practicing walking-meditation (caṅkramana) for ninety days without sleep” has been considered the main feature of pratyutpanna samādhi and even the requisite for achieving it ever since pratyutpanna samādhi began its circulation in China and Japan. This misconception has caused the meaning, goal and even the method of practice of pratyutpanna samādhi to become more obscure and misdirected. In order to correct this misconception and to reveal the true meaning of pratyutpanna samādhi, I will explore how the meaning of śūnya evolved from the original Buddhism to early Mahāyāna Buddhism so that we can see the lineage and the development of the concept of śūnya that Pratyutpanna-Buddha-Saṃmukhāvasthita-Samādhi-Sūtra represents. Furthermore, I will also make a philosophical study of the concept of śūnya illustrated by pratyutpanna samādhi to derive that pratyutpanna samādhi should be categorized as Thusness Buddha-Recollection and Mahāyāna śūnya samādhi and point out the link between “nimitta/nāman”and “anupalabdhi” highlighted in early Mahāyāna Buddhism. I therefore conclude that Pratyutpanna-Buddha-Saṃmukhāvasthita-Samādhi-Sūtra explicates the concepts of śūnya of the prajñāpāramitā literature such as “all is empty”, “the very nature of existence is empty”, “without inherent nature”. I will explain wh
