GEIGER is a new R-based software package for analyzing phylogenetic comparative data, focusing on evolutionary radiations. It offers simulation, parameter estimation, and statistical hypothesis testing. GEIGER complements existing packages like APE, apTreeshape, OUCH, and LASER. It can simulate phylogenetic trees and phenotypic characters, allowing for the analysis of statistical power of comparative methods. GEIGER also enables tree pruning to address incomplete sampling, which can bias analyses. It includes a simulation procedure to correct for bias in the gamma statistic, which measures diversification rates. GEIGER can simulate discrete and continuous character evolution on phylogenetic trees, including multivariate Brownian motion models. It estimates parameters related to species diversification and character evolution, such as net diversification rates. GEIGER provides hypothesis testing functions, including tests for clade diversity and disparity-through-time analysis. It also supports phylogenetic ANOVA or MANOVA using simulation. GEIGER is freely available in R and is cross-platform, facilitating further software development. The software is supported by various funding sources and has been acknowledged for its contributions to phylogenetic analysis.GEIGER is a new R-based software package for analyzing phylogenetic comparative data, focusing on evolutionary radiations. It offers simulation, parameter estimation, and statistical hypothesis testing. GEIGER complements existing packages like APE, apTreeshape, OUCH, and LASER. It can simulate phylogenetic trees and phenotypic characters, allowing for the analysis of statistical power of comparative methods. GEIGER also enables tree pruning to address incomplete sampling, which can bias analyses. It includes a simulation procedure to correct for bias in the gamma statistic, which measures diversification rates. GEIGER can simulate discrete and continuous character evolution on phylogenetic trees, including multivariate Brownian motion models. It estimates parameters related to species diversification and character evolution, such as net diversification rates. GEIGER provides hypothesis testing functions, including tests for clade diversity and disparity-through-time analysis. It also supports phylogenetic ANOVA or MANOVA using simulation. GEIGER is freely available in R and is cross-platform, facilitating further software development. The software is supported by various funding sources and has been acknowledged for its contributions to phylogenetic analysis.