Buoyancy frequency and shear were used to estimate spatial and temporal variations in Richardson number, Ri, on Georges Bank. Calculations were based on CTD and ADCP data from 41 stations occupied repeatedly over 17 cruises during winter and spring, 1995--1999. Stations were grouped into five spatial averaging regions, two depth zones, and two seasons. Average Ri ranged from 0.01 to 1.63 with a general tendency of increasing Ri with total water depth. Significant differences in average Ri between the two seasons and two depth zones were also found. These differences were largely due to variations in buoyancy frequency, and to a lesser degree due to variations in shear. Our results offer an empirical context for examining spatial and temporal variability of vertical mixing on the Bank.