There can only be two possible outcomes, 'success' and 'fail' (e.g heads or tails) There is a fixed number of trialsThe probabilities of 'success' and 'fail' are constant and stay the same in each trial (e.g the probability of rolling a 3 on a dice is always 1/6)The result of each trial is independent of the result of each previous trial (e.g getting a heads at one trial does not change the likelihood of getting a heads at the next trial, the probability is still 0.5)