This chapter concerns the philosophy underlying the Biodynamic model of osteopathy in the cranial field (BOCF). To do this we employ a Hegelian dialectic, a weave of BOCF principles with BOCF science, presented within an historical context. We will compare biomechanical OCF with Biodynamic OCF, or "left-brained versus right-brained cranial" as Fred Mitchell likes to quip. No treatment methods will be described here. Note that certain words in this article will be capitalized, indicating the usage of a defined BOCF meaning, not a standard dictionary sense. BOCF's legacy extends back to Hippocrates, as reflected in the Hippocratic Oath's axiom "do no harm," and its concern for our triune (body-mind-spirit) integrity. Threads of Paracelcus-style empiricism and Avicennian experimentalism colour the BOCF tapestry. The foundation of BOCF, however, is firmly grounded in the philosophy and practice of three osteopathic teacher-physicians, evolving from three lifetimes spent in general medical practice, working alongside the self-balancing, self-healing principles present in their patients. The first of these teacher-physicians is Andrew Taylor Still (1828-1917), who founded osteopathy in 1874. Dr. Still sought "the Health" in his patients, which was always present no matter how sick his patients presented. This concept was fundamental to Still's hands-on approach to care. "I love my patients," he declared, "I see God in their faces and their form" (Still 1908). The physician's task, Still always reminded his students, was to remove with gentleness all perceived mechanical obstructions to the free-flowing rivers of life (blood, lymph, and cerebro-spinal fluid). Nature would then do the rest. Still formulated innovative concepts regarding the cranium, the cranial nerves, and he famously proclaimed, "the cerebrospinal fluid [CSF] is the highest known element that is contained in the human body" (Still 1899). His treatment techniques included gentle pressure on cranial bones, for example in the treatment of pterygium (Still 1910). The second of these teacher-physicians is William Garner Sutherland (1873-1954), who founded Osteopathy in the Cranial Field (OCF). Dr. Sutherland was a student of Still and became imbued with Still's thinking, methods, and practice. Sutherland formulated his first cranial hypothesis as a student in 1899 while examining a temporal bone from a disarticulated skull. The thought struck him that its edges were bevelled like the gills of a fish, as if part of a respiratory system. Sutherland's 1899 revelation initiated a life-long evolution of thought, described in subsequent sections of this chapter. The third teacher-physician is James S. Jealous (1943-) whose Biodynamic Model of OCF (BOCF) has attracted great interest and controversy within the profession. Jealous adapted the term Biodynamic from his study of the German embryologist Erich Blechschmidt, and not from the Swiss philosopher Rudolf Steiner, although Steiner's Biodynamic concepts resonate with BOCF principles. For over 30 years Dr. Jealous has compiled oral histories from Sutherland's students, and he continues to research Sutherland's writings (both published and unpublished). This "work with the elders" enabled Jealous to compile an authoritative chronology of Sutherland's journey. Thus BOCF dedicates itself to the perceptual odyssey where Sutherland left off at the end of his life.