Predoctoral Training Program in Biological Data Science (BDS) - Biology has become a data-driven, quantitative science, leading to an enormous demand for deeply trained scientists at the interface of biology and computing who engage in interdisciplinary collaboration. The Predoctoral Training Program in Biological Data Science (BDS) at the University of Colorado Boulder BioFrontiers Institute is a student-centered, interdisciplinary training program aimed at generating scientists prepared for both the challenges of big data and productive careers in biological data science. Training faculty are an outstanding, internationally recognized group of 25 researchers from five departments across two colleges, who leverage data science approaches towards research in the biomedical sciences. The program will train students in core principles of data science, including data management, analysis, visualization, as well as effective communication and collaboration, with a particular focus on rigor and reproducibility in big data research and usage. We request support for five positions in year one, 10 positions in subsequent years. Promising trainees will be selected at the end of their first year for support in years 2-3. BDS program elements include cross-department coursework, data science skill building, workshops, supergroup meetings, and seminars that collectively engage students. Coursework on responsible conduct of research and a rigor and reproducibility workshop in data science will instill students with the expectations and skillset for conducting data science research with high ethical standards. A network of academic, social, financial, and mental health resources will be in place to support interdisciplinary trainees. Trainee mentoring through peers and academic (co-)advising, formal industry partnerships and mentorship, thesis committees, and interdisciplinary collaborations also support trainee progress. The training program fosters a research group that would otherwise not have an environment to access guided training in comprehensive biological data science. BDS incorporates academia and industry perspectives to guide curriculum, assist students in building meaningful scientific networks, and enable successful career development.