  This is a survey paper on Poisson approximation using Stein's method of
exchangeable pairs. We illustrate using Poisson-binomial trials and many
variations on three classical problems of combinatorial probability: the
matching problem, the coupon collector's problem, and the birthday problem.
While many details are new, the results are closely related to a body of work
developed by Andrew Barbour, Louis Chen, Richard Arratia, Lou Gordon, Larry
Goldstein, and their collaborators. Some comparison with these other approaches
is offered.
