Thirty years ago, theorists showed that a properly designed combination of incident waves could be fully transmitted through (or reflected by) a disordered medium, based on the existence of propagation channels which are essentially either closed or open (bimodal law). In this Letter, we study elastic waves in a disordered waveguide and present a direct experimental evidence of the bimodal law. Full transmission and reflection are achieved. The wave-field is monitored by laser interferometry and highlights the interference effects that take place within the scattering medium. PACS numbers: 42.25.Dd, 43.20.Gp, 42.25.Bs Light travelling through thick clouds, electrons conducting through metals or seismic waves in the earth crust are all examples of waves propagating through disordered materials. Energy transport by waves undergoing strong scattering is usually well described by diffusion theory. However, this classical picture neglects interference effects that may resist the influence of disorder. Interference is responsible for fascinating phenomena in mesoscopic physics. On the one hand, it can slow down and eventually stop the diffusion process, giving rise to Anderson localization [1,2]. On the other hand, it can also help waves to find a way through a maze of disorder [3]. Actually, a properly designed combination of incident waves can be completely transmitted through a strongly scattering medium, as suggested by Dorokhov and others more than twenty years ago [4][5][6][7]. This prediction has recently received a great deal of attention mostly due to the emergence of wave-front shaping techniques in optics [8].In order to address the open channels (i.e., to achieve full energy transmission) across a disordered wave guide, one has to perform a complete measurement of the scattering matrix S. The S-matrix relates the input and output of the medium [7]. It fully describes wave propagation across a scattering medium. It can be generally divided into blocks containing transmission and reflection matrices, t and r, with a certain number N of input and output channels. Initially, random matrix theory (RMT) has been successfully applied to the transport of electrons through chaotic systems and disordered wires [7]. However, the confrontation between theory and experiment has remained quite restrictive since specific input electron states cannot be addressed in practice. On the contrary, a coherent control of the incident wave-field is possible in classical wave physics. Several works have demontrated the ability of measuring the S-matrix, or at least some of its subspaces, in disordered media, whether it be in acoutics [9-11], electromagnetism [12,13] or optics [14][15][16][17].The existence of open channels has been revealed by investigating the eigenvalues T of the Hermitian matrix tt † . Theoretically, their distribution should follow a bimodal law [4,5,7], exhibiting two peaks. The highest one, around T ∼ 0, correspond to closed (i.e. strongly reflected) eigenchannels. At the other end of the spectrum (T ∼ 1)...