When looking at two random variables simultaneously it has to be examined first with which probabilities do value combinations occur. This leads to the common probability functions. Then the attention focuses mainly on the connection between the two random variables. The connection or of the absence of any connection therefore make up the central parts of this module. For this, marginal distributions and conditional distributions are needed as further concepts. These, however, are also interesting themselves. After all, the distributions of combinations of random variables depend on their common probability function.