Twenty years after the first joint detections of gravitational lensing by large-scale structure (cosmic shear), current galaxy lensing surveys are placing impressive constraints on our understanding of structure growth over cosmic time, even rivaling the precision delivered by cosmic microwave background experiments. I will introduce how the weak gravitational lensing phenomenon works and give a broad overview of the analysis process. Using recent results from the Dark Energy Survey as context, I will highlight the most precarious moving parts of the analysis in terms of potential sources of systematic error. I will conclude with a look forward to future lensing experiments such as the ground-based Rubin Observatory and space-based Euclid and Roman missions.