Investigating the interaction between spreading processes in complex networks is one of the most important challenges in network science. However, whether we would like to know how the information campaign will affect virus spreading or how the advertising campaign of the new iPhone will affect the sales of Samsung phones, we need an environment that will allow us to evaluate under what conditions our spreading campaign will be effective. Network Diffusion is a Python package that should help do that. In this paper, we introduce its operating principle and main functionalities, including simple examples of simulations that can be performed using it.