In this talk, I will focus on a new method we have developed to investigate bacterial chemotaxis—how cells sense and swim along gradients of chemicals. Chemotaxis of the bacterium Escherichia coli serves as a model for the way living cells respond and adapt to changes in their environment. Although the chemotactic response has been well characterized at the level of the individual flagellar motors that propel the cell and in populations of swimming cells, precise quantification at the level of the single cell has not yet been possible. Optical traps or “tweezers”, which utilize focused light to trap and manipulate microscopic objects, have emerged as a powerful tool in molecular biology, biochemistry and biophysics. Here we use a novel optical trapping technique to characterize the swimming behavior of individual E. coli and their response to sudden changes in the chemical environment. I discuss our findings in the context of accepted theoretical models of the chemotaxis network, and suggest how these findings provide clues to an improved understanding of chemotaxis.