Niels Stensen (1638–1686) was a prominent Danish scientist who laid the foundations of paleontology, geology, and crystallography. He undertook a personal search for the truth, rejecting many assumptions of his time, and he struggled to acquire a firm foundation of knowledge based on close observation and rigorous experimentation. Niels Stensen is known eponymously for the discovery of the duct of the parotid gland (ductus stenonianus) but most clinicians are not familiar with his contributions to anatomy beyond his studies on the glands. In 1665, he delivered a lecture in Paris on the anatomy of the brain, the Discours sur l'anatomie du cerveau (“A Dissertation on the Anatomy of the Brain”), which is a seminal investigation on methods in neuroscience. His scientific letter on a hydrocephalic calf represents an early pathophysiological investigation on hydrocephalus. In 1667 Stensen converted to Catholicism and in 1677 he was consecrated titular bishop of Titiopolis. He spent the last years of his life in poverty and traveled continuously trying to bring back northern Europe to Catholicism. This essay highlights the life and the scientific contributions of Niels Stensen, with emphasis on his contributions to neuroscience.