* Structured demographic models offer powerful methods for addressing important questions in ecology and evolution. * Integral Projection Models (IPMs) are related to classic matrix models, but are more appropriate for modelling structured populations when the variable describing individuals' demography is continuous (e.g. size, weight, etc.). * We present IPMpack, a free open-source software (R) package for building IPMs. The package estimates key population characteristics from IPMs, such as population growth rate in both deterministic and stochastic environments, age-specific trajectories of survival and reproduction, and sensitivities and elasticities to changes in underlying vital rates. * IPMpack can be used for species across a range of life cycle complexity and can include continuous and discrete (e.g. seed bank, hibernation) state variables, as well as environmental covariates of interest. Methods for diagnostics, sensitivity analyses, plotting, model comparison and many other features allow users to move from data input through analysis to inference using an array of internal functions. * IPMpack fills a need for readily usable tools for constructing and analysing IPMs and is designed to facilitate their use for experts and open up their use for those researchers who have little experience in the details of population models. A standardized IPM modelling framework will also facilitate cross-study and cross-species comparative demography, encouraging the exploration of broader ecological and evolutionary questions that can be addressed by population models.
