FEBio is a nonlinear implicit finite element (FE) framework designed for computational solid biomechanics. It addresses the limitations of existing commercial software by providing a tailored environment for biomechanical modeling. The software offers modeling scenarios, constitutive models, and boundary conditions relevant to various biomechanical applications. FEBio is open-source, written in C++, and optimized for performance on modern computer architectures. It includes verification tools and a suite of benchmark problems to validate its accuracy against analytical solutions and established FE codes. FEBio is supported by PREVIEW and POSTVIEW for preprocessing and postprocessing. The paper presents the theoretical basis of FEBio, its features, and results from verification problems. FEBio supports both quasi-static and dynamic analyses, a wide range of constitutive models, and various boundary conditions. It uses an implicit time integration scheme and includes contact algorithms for rigid and deformable materials. The software is verified against analytical solutions and results from other FE codes, demonstrating high accuracy. FEBio is also used for research applications, such as modeling the human inferior glenohumeral ligament. The paper highlights the importance of verification in computational biomechanics and the ongoing development of FEBio to support future research. FEBio provides a flexible and extensible framework for computational biomechanics, with a focus on accuracy and performance.FEBio is a nonlinear implicit finite element (FE) framework designed for computational solid biomechanics. It addresses the limitations of existing commercial software by providing a tailored environment for biomechanical modeling. The software offers modeling scenarios, constitutive models, and boundary conditions relevant to various biomechanical applications. FEBio is open-source, written in C++, and optimized for performance on modern computer architectures. It includes verification tools and a suite of benchmark problems to validate its accuracy against analytical solutions and established FE codes. FEBio is supported by PREVIEW and POSTVIEW for preprocessing and postprocessing. The paper presents the theoretical basis of FEBio, its features, and results from verification problems. FEBio supports both quasi-static and dynamic analyses, a wide range of constitutive models, and various boundary conditions. It uses an implicit time integration scheme and includes contact algorithms for rigid and deformable materials. The software is verified against analytical solutions and results from other FE codes, demonstrating high accuracy. FEBio is also used for research applications, such as modeling the human inferior glenohumeral ligament. The paper highlights the importance of verification in computational biomechanics and the ongoing development of FEBio to support future research. FEBio provides a flexible and extensible framework for computational biomechanics, with a focus on accuracy and performance.