In this paper, the authors describe how two institutions are helping their undergraduate biology students build quantitative competencies. Incorporation of quantitative skills and reasoning in biology are framed through a discussion of two cases that both concern introductory biology courses, but differ in the complexity of the mathematics and the type of changes involved. First, at the University of Maryland-College Park, MathBench Biology Modules (via an interactive Web-based instructional service) are providing supplemental materials to illustrate and develop quantitative competencies basic to biology. The second example, at Davidson College, uses a unique text to introduce a wide range of students, including those with no calculus experience, to challenging mathematical concepts in biology. The textbook emphasizes learning through modeling and data analysis, activities that are integral to developing understanding in biology. (Contains 2 tables.)