ExoTR (Exoplanetary Transmission Retrieval) interprets exoplanetary transmission spectra using a Bayesian inverse retrieval algorithm. The code can be used in two ways; the first is by leveraging the physics forward model only to generate synthetic planetary atmospheric transmission spectra (including the addition of errorbars). The second way is by using a retrieval routine based on nested sampling (i.e., MultiNest (ascl:1109.006)) to extract physical and chemical information from the input transmission spectra.