Motivation:The ability to simulate epidemics as a function of model parameters allows insights that are unobtainable from real datasets. Further, reconstructing transmission networks for fast-evolving viruses like HIV may have the potential to greatly enhance epidemic intervention, but transmission network reconstruction methods have been inadequately studied, largely because it is difficult to obtain "truth" sets on which to test them and properly measure their performance.Results: We introduce FAVITES, a robust framework for simulating realistic datasets for epidemics that are caused by fast-evolving pathogens like HIV. FAVITES creates a generative model to produce contact networks, transmission networks, phylogenetic trees, and sequence datasets, and to add error to the data. FAVITES is designed to be extensible by dividing the generative model into modules, each of which is expressed as a fixed API that can be implemented using various models. We use FAVITES to simulate HIV datasets and study the realism of the simulated datasets. We then use the simulated data to study the impact of the increased treatment efforts on epidemiological outcomes. We also study two transmission network reconstruction methods and their effectiveness in detecting fast-growing clusters.Availability and implementation: FAVITES is available at https://github.com/niemasd/FAVITES, and a Docker image can be found on DockerHub (https://hub.docker.com/r/niemasd/favites).Redd, 2014). More recently, these methods have become widely used at both local and global scale . Nevertheless, several questions remain to be fully answered regarding the performance of these methods. It is not always clear which method/setting combination performs best for a specific downstream use-case or for specific epidemiological conditions. More broadly, the effectiveness of these methods in helping achieve public health goals is the subject of ongoing clinical and theoretical research.Accuracy of transmission networks is difficult to assess because the true order of transmissions is not known. Moreover, predicting the impact of parameters of interest (e.g., rate of treatment) on the epidemiological outcomes is difficult. In simulations, in contrast, the ground truth is known and parameters can be easily controlled. The simulation of transmission networks needs to combine models of social network, transmission, evolution, and ideally sampling biases and errors (Villandre et al., 2016) .We introduce FAVITES (FrAmework for VIral Transmission and Evolution Simulation), which can simulate numerous models of contact networks, viral transmission, phylogenetic and sequence evolution, data (sub)sampling, and real-world data perturbations, and which was built to be flexible such that users can seamlessly plug in statistical models at every step of the simulation process. Previous attempts to create an epidemic simulation tool include epinet (Groendyke et al., 2012), TreeSim (Stadler and Bonhoeffer, 2013), outbreaker (Jombart et al., 2014), seedy (Worby and Read, 2015), and...