We present a weak lensing detection of filamentary structures in the cosmic web, combining data from the Kilo-Degree Survey, the Red Cluster Sequence Lensing Survey and the Canada-France-Hawaii Telescope Lensing Survey. The line connecting luminous red galaxies with a separation of 3−5h−1Mpc is chosen as a proxy for the location of filaments. We measure the average weak lensing shear around ∼11,000 candidate filaments selected in this way from the Sloan Digital Sky Survey. After nulling the shear induced by the dark matter haloes around each galaxy, we report a 3.4σ detection of an anisotropic shear signal from the matter that connects them. Adopting a filament density profile, motivated from N-body simulations, the average density at the centre of these filamentary structures is found to be 15±4 times the critical density.