The purpose of this study is to examine the references to sleep in the early Buddhist texts in order to comprehensively examine what the Buddha has to teach us about sleep. The content of this study examines the texts’ references to sleep from a dharmic perspective. Rather than simply presenting a view of sleep, it analyzes what this means in terms of practice. In addition, the relevance to practice is made more concrete through the discussion of bad tendencies(隨眠) as afflictions. Bad tendencies as afflictions are usually referred to as anusaya, meaning latent afflictions. It is distinct from ordinary sleep (睡眠). However, anusaya is derived from the word sayati, which means sleep. Therefore, the Chinese character for sleep(眠) is also used. Thus, lack of knowledge of the sacred teachings is sometimes described as “falling asleep and not waking up. The results of this study show that in the early sutras, sleep is explicitly linked to practice. In order to sleep well, one must abandon the desire-attached form of life and establish proper sati. The establishment of sati(正念) and sampajñāna(正知), or stillness and knowledge, is closely related to “sleeping joyfully and waking joyfully. Thus, in Buddhism, dreamless sleep and sound sleep can be understood as one of the outcomes of the eightfold sammāsati for those who practice correctly.