This paper describes the drc package for R, which allows simultaneous fitting of multiple non-linear regression models, with a focus on dose response curve analysis. The package is designed for bioassay analysis, where the response of organisms to different doses of a compound is studied. It supports various non-linear models, including logistic, Weibull, and Brain-Cousens models, which are used to describe dose-response relationships. The package provides functions for model fitting, parameter estimation, and comparison of parameters across different curves. It also includes tools for calculating effective dosages (ED) and selectivity indices (SI), which are used to compare the potency and selectivity of compounds. The package is open-source and freely available, and it is implemented in R, a statistical programming language. The paper illustrates the use of the package through examples, showing how to fit models to data, perform statistical tests, and interpret results. The package is particularly useful for analyzing bioassay data where multiple dose-response curves are involved, and it allows for the comparison of parameters across different curves. The drc package provides a flexible and powerful tool for non-linear regression analysis in bioassay studies.This paper describes the drc package for R, which allows simultaneous fitting of multiple non-linear regression models, with a focus on dose response curve analysis. The package is designed for bioassay analysis, where the response of organisms to different doses of a compound is studied. It supports various non-linear models, including logistic, Weibull, and Brain-Cousens models, which are used to describe dose-response relationships. The package provides functions for model fitting, parameter estimation, and comparison of parameters across different curves. It also includes tools for calculating effective dosages (ED) and selectivity indices (SI), which are used to compare the potency and selectivity of compounds. The package is open-source and freely available, and it is implemented in R, a statistical programming language. The paper illustrates the use of the package through examples, showing how to fit models to data, perform statistical tests, and interpret results. The package is particularly useful for analyzing bioassay data where multiple dose-response curves are involved, and it allows for the comparison of parameters across different curves. The drc package provides a flexible and powerful tool for non-linear regression analysis in bioassay studies.