The subject of this thesis is the simulation of X-ray cluster surveys and related issues, with a focus on the research that can be conducted with the International X-ray Observatory (IXO), or a similar next-generation X-ray observatory. A general purpose X-ray image simulator has been developed. It uses a modern cosmological simulation and cluster scaling relations to produce simulated cluster images that are well motivated by theory and observation. A distribution of point sources and various instrumental effects are also included. The simulator is complemented by a source identification method. The IXO selection function is mapped over a varying surface brightness parameter space. Simulated IXO surveys are used to explore the biases present in X-ray cluster surveys. These reveal that it is necessary to correct for biases using a detailed and carefully applied selection function to recover the true evolution of the luminosity-temperature relation. This is crucial for shallow surveys. Simulations of IXO using different angular resolutions are found to have only a minor effect on the number and distribution of detected clusters.