How do I know when I should be using the Poisson distribution?

To identify a Poisson distribution question, remember that in a Poisson distribution... Events occur independently of each other Events occur at a constant rate Events occur singly (that is, two can't happen at once) An example could be 'the number of cars passing your house every hour' because the appearance of a car doesn't change the probability of another car passing, they are likely to pass at a constant rate, and two cars cannot pass at the same time.