We examine the stability of the elliptic solutions of the focusing nonlinear Schrödinger equation (NLS) with respect to subharmonic perturbations. Using the integrability of NLS, we discuss the spectral stability of the elliptic solutions, establishing that solutions of smaller amplitude are stable with respect to larger classes of perturbations. We show that spectrally stable solutions are orbitally stable by constructing a Lyapunov functional using higher-order conserved quantities of NLS.1. Spectral stability is considered in Section 3. This is motivated by considering the simpler case of the well-known Stokes waves in Section 3.2. For these solutions, all operators involved have constant coefficients, and all calculations are explicit. We get to the spectrum of the operator obtained by linearizing about a solution through its connection with the Lax spectrum. To this end, we introduce the Lax pair and its spectrum in Section 3.3. The results in Section 3.3.1 are from [16] while the results in Section 3.3.2 and all subsequent sections are new. Section 3.4 contains our main spectral stability result: solutions are spectrally stable with respect to subharmonic perturbations if the solution 1