GEIGER is a new software package written in the R language, designed to analyze phylogenetic comparative data and detect evolutionary radiations. It can simulate phylogenetic trees and phenotypic characters, estimate key parameters associated with species diversification and character evolution, and perform various statistical hypothesis tests. GEIGER complements other packages like APE, apTreeShape, OUCH, and LASER, and can be used to investigate the statistical power of comparative approaches. The software is freely available through the Comprehensive R Archive Network (CRAN). Key features include tree simulation under a birth-death model, tree pruning for incomplete sampling, simulation of discrete and continuous character evolution, parameter estimation for net diversification rates, and hypothesis testing for clade diversity and character evolution.GEIGER is a new software package written in the R language, designed to analyze phylogenetic comparative data and detect evolutionary radiations. It can simulate phylogenetic trees and phenotypic characters, estimate key parameters associated with species diversification and character evolution, and perform various statistical hypothesis tests. GEIGER complements other packages like APE, apTreeShape, OUCH, and LASER, and can be used to investigate the statistical power of comparative approaches. The software is freely available through the Comprehensive R Archive Network (CRAN). Key features include tree simulation under a birth-death model, tree pruning for incomplete sampling, simulation of discrete and continuous character evolution, parameter estimation for net diversification rates, and hypothesis testing for clade diversity and character evolution.