Research on transposable elements began nearly 100 years ago with classical genetic experiments. Remarkably, many of the activities of transposable elements, such as the ability to transpose, to induce chromosome rearrangements, to undergo cycles of activity and inactivity, and to affect expression of neighboring genes, were described by geneticists long before transposons were molecularly isolated. This chapter traces the historical roots of transposable element research, describing the scientists, their observations, and interpretations as they sought to understand the enigma of transposable elements.