This paper discusses how to get secure random numbers for your application. We describe how to take a single, secure, random number (a seed), and stretch it into a big stream of random numbers using a secure pseudo-random number generator. We talk about how to get random data in lots of different representations (e.g., an integer in a particular range or a printable string). We also discuss how to get real randomness in an environment that is fundamentally deterministic, and we give advice on figuring out how to estimate how much randomness exists in a piece of data.