Le Targat co-leads SYRTE's Optical Frequency Metrology team, which built and continuously operates two independent strontium optical lattice clocks alongside a mercury lattice clock, comparing them at the 10^-16 to 10^-17 level and to SYRTE's caesium fountain primary standards. This work underpins the prospective redefinition of the SI second on an optical transition and supports frequency-transfer, geodesy and fundamental-physics tests via fiber links to other French metrology laboratories.