jats:titleAbstract</jats:title> jats:sec jats:titleMotivation</jats:title> jats:pMendelian randomization methods that estimate non-linear exposure-outcome relationships typically require individual-level data. This package implements non-linear Mendelian randomization methods using stratified summarized data, facilitating analyses where individual-level data cannot easily be shared, and additionally increasing reproducibility as summarized data can be reported. Dependence on summarized data means the methods are independent of the form of the individual-level data, increasing flexibility to different outcome types (such as continuous, binary or time-to-event outcomes).</jats:p> </jats:sec> jats:sec jats:titleImplementation</jats:title> jats:pSUMnlmr is available as an R package (version 3.1.0 or higher).</jats:p> </jats:sec> jats:sec jats:titleGeneral features</jats:title> jats:pThe package implements the previously proposed fractional polynomial and piecewise linear methods on stratified summarized data that can either be estimated from individual-level data using the package or supplied by a collaborator. It constructs plots to visualize the estimated exposure-outcome relationship, and provides statistics to assess preference for a non-linear model over a linear model.</jats:p> </jats:sec> jats:sec jats:titleAvailability</jats:title> jats:pThe package is freely available from GitHub [https://github.com/amymariemason/SUMnlmr].</jats:p> </jats:sec>