Strong lensing systems provide a unique laboratory in which to study the fundamental physics of the Universe and the evolution of galaxies. Two next-generation space-based surveys, the Chinese Space Station Telescope survey (CSS-OS) and the ESA Euclid mission, will increase the number of known strong lenses by more than two orders of magnitude, and survey them all with high-resolution imaging in near-UV to infrared wavelengths. We propose an international team comprising experts in strong lensing from both missions, to explore the potential scientific return of a joint analysis of the combined data. Specifically, we will address the following key problems:

1) How to efficiently search for strong lens systems in Euclid + CSS-OS data.

2) How to model the distribution of dark matter in lensing systems with multi-color imaging.

3)Optimum synergy between the two survey designs.