胎息，爲煉氣的上乘境界，是希望人的呼吸達到「真息」的境地；而所謂的真息是「無息之息」，以現代術語形容，可稱爲「體呼吸」。道教胎息術源遠流長，白先秦時期，老子、莊子及戰國行氣銘，間有對呼吸方式的描述，而秦漢以後，以道藏中氣功相關部分論述最詳。「胎息」的狀態，丹書上形容是：「外想不入，內想不出；全元氣，守真一。」而要達到胎息的境界，並不是一蹴可幾的；它必須經由積精累氣，涵藏體內的真氣直至某一程度，並藉由行氣導引，至使百脈關節暢通，並且在無思無慮的狀態下，使形神與自然合一。本論文嘗試將傳統上道家，道教中有關「胎息」的論述，加以歸納、分析、整理；並結合現代人及個人實修經驗，加以探討印證，希望對於「胎息」的意義與性質，有較全面而深入的瞭解。

Fetal Breathing stands for the ultimate level of Chi practice that calls for the regulation of man's breathing into the status of "real breathing." The so-called real breathing indicates to "Breathing of no breath," which, in modern terms, should be called the "body breath." The "theory of fetal breathing" can be traced long back into the history all the t ay from before Chin Dynasty. There are quite a number of descriptions on the methods of breathing in the writings of Lao Tzu, Chuang Tzu, and then in the Inscription of Chi Operation from the Warring-States Era. After Chin and Han Dynasties, the issue was fully elaborated and stated in the section of Taoism that is related to Chi Kung. The state of fetal breathing, according to the description in Taoist cinnabar writ, should be: "the outer thoughts will not come in, the inner thoughts will not go out, the Chi is being completed, and the truthful oneness is being kept." There is no way one can achieve the state of fetal breathing immediately, it takes accumulation of energy and Chi. saving and keeping the true Chi in one's body until it reaches a certain level, then through proper exercise and guidance, the Chi will go through and smooth out all pulses and joints in the body, and then one's form, spirit, and Nature can become one under the condition when one feels carefree and free-of-worries. Essays and discourses about fetal breathing that are mentioned in traditional Tao theories and Taoist beliefare inducted, analyzed and assorted in this research paper. The results will then be discussed and proved by individual practices in modern context. I hope the overall significance and the nature of fetal breathing can be more profoundly understood through this effort.