Bollinger Bands, created by John Bollinger, are a popular range indicator traders and investors use to measure market volatility. The bands are based on a moving price average and are drawn at a certain number of standard deviations away from the average. As a measure of volatility, the bands self-adjust, expanding during high volatility and contracting during periods of low volatility. This makes them useful for identifying potential trading opportunities and managing risk in changing market conditions.