Henri Poincare's work on mathematical features of the Lorentz transformations was an important precursor to the development of special relativity. In this paper I compare the approaches taken by Poincare and Einstein, aiming to come to an understanding of the philosophical ideas underlying their methods. In section (1) I assess Poincare's contribution, concluding that although he inspired much of the mathematical formalism of special relativity, he cannot be credited with an overall conceptual grasp of the theory. In section (2) I investigate the origins of the two approaches, tracing differences to a disagreement about the appropriate direction for explanation in physics; I also discuss implications for modern controversies regarding explanation in the philosophy of special relativity. Finally, in section (3) I consider the links between Poincare's philosophy and his science, arguing that apparent inconsistencies in his attitude to special relativity can be traced back to his acceptance of a `convenience thesis' regarding conventions.