The original body of the book was inspired by a series of lectures on Isvarakrsna's Samkhya Karika given by Swami Bawra. The presentation includes an English translation of the Samkhya Karika hymns and the Bhasya of Gaudapadacarya. The revised edition includes an introduction to the oral tradition of Samkhya, including the story of Kapila from a Purana and a presentation of the surviving sutras of Pancasikha's Sastitantra. This lost text was the first compilation of Samkhya and was used by Isvarakrsna in his Samkhya Karika. The unified concept of Nature and Spirit as two phases of one source is found in this early tradition, and the intimacy of Samkhya with Yoga is displayed. Samkhya teaches that Nature is real but has qualities that are different from Spirit. Spirit is sentient, infinite and unchanging. Nature is insentient, finite and exists in ever-changing forms. With proper knowledge and repeated practice, we can change our habits of thought and realize the underlying constancy of spirit.