2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/1967I review simultaneous constraints on the cosmological parameters lambda_0 and Omega_0 from gravitational lensing. The emphasis is on systematic extragalactic surveys for strong gravitational lenses, mainly the largest and best-defined such survey, JVAS/CLASS.10 pages, LateX, 4 PostScript plots included in 3 figures; invited contribution to appear in the proceedings of IAU Symposium 201 `New Cosmological Data and the Values of the Fundamental Parameters' (A. Lasenby and A. Wilkinson, eds.). Related papers at http://gladia.astro.rug.nl:8000/ceres/papers/papers.html . Paper version available on requestAstrophysicstext