COMPoissonReg is an R package which supports Conway-Maxwell Poisson (CMP) and Zero-Inflated Conway-Maxwell Poisson (ZICMP) models. This vignette describes fundamental computational details, especially those involving the normalizing constant and related quantities. The CMP normalizing constant does not have a general closed form; furthermore, it requires care to handle numerically as its magnitude can vary greatly with changes in the parameters. Primary COMPoissonReg functions are demonstrated with examples, including those implementing basic distribution functions and regression modeling.