Weak gravitational lensing (WL) analysis measures slight shape distortion of background galaxies due to a foreground lens (e.g., galaxy cluster). WL analysis directly provides information on the lens’s mass distribution and the most accurate mass estimate, especially for high-redshift and/or merging galaxy clusters. This is because WL does not rely on the hydrostatic equilibrium assumption. In this talk, I summarize my PhD thesis research, determining the masses of about 40 high-redshift (0.8 < z < 1.8) galaxy clusters using WL analysis. I used archival deep optical and near-infrared imaging data observed by the Hubble Space Telescope. I firstly present detailed WL results of two massive high-redshift galaxy clusters, SPT-CL J2106-5844 (z=1.13) and ACT-CL J0102-4915 (z=0.87), and show that the two clusters are compatible with ΛCDM, although the two systems are indeed massive. Then, I construct a WL mass versus X-ray temperature scaling relation for about 40 high-z clusters. My WL sample size is the largest at z > 0.8 to date and includes the highest redshift cluster (JKCS 041 at z=1.8). The mass scaling relation for high-z clusters follows self-similarity. This will serve as a calibrator to determine the accurate masses of more than 1000 high-z clusters discovered in various surveys. I also compare the observed mass-concentration (M-c) relation with the theoretical prediction at high-redshift. The best-fit M-c relation from observation shows a steeper slope than the prediction of N-body simulations. Lastly, I introduce the Euclid space telescope, the first WL survey in space, launched in 2024. I briefly explain the mission objectives, survey design, and my role in the mission.