[en] Since the details of the gravitational lensing effect depend on the cosmological model, it offers a means of determining the cosmological parameters H[SUB]0[/SUB], λ[SUB]0[/SUB] and Ω[SUB]0[/SUB] by comparing expectations from different cosmological models with observations. Advantages of using gravitational lensing to learn about the cosmological model include the fact that it is based on relatively well understood astrophysics and that it makes use of information from an intermediate redshift range, complementing tests which use information primarily from the low-redshift (e.g. cosmic flows) or high-redshift (e.g. cosmic microwave background fluctuations) regimes. I review simultaneous constraints on the cosmological parameters λ[SUB]0[/SUB] and Ω[SUB]0[/SUB] from gravitational lensing. (Constraints on H[SUB]0[/SUB] are discussed in a previous talk.) The emphasis is on systematic extragalactic surveys for strong gravitational lensing, mainly the largest and best-defined such survey, JVAS/CLASS. However, other methods of constraining λ[SUB]0[/SUB] and Ω[SUB]0[/SUB] using (mostly strong) gravitational lensing are also discussed. After briefly reviewing the basic theory and history of the subject, I present the currently available constraints and briefly (since this is covered in later talks) touch on joint constraints with other cosmological tests. Finally, I discuss systematic errors and prospects for the future.
