This is a review paper, with focus both on general theoretical and analytical issues in fossil and molecular dating, and on the specific case of Annonaceae, a pan-tropical family of flowering plants. It represents a collaborative work between Michael Pirie (molecular dating), and Jim Doyle (fossils). We described the principles underlying the process of estimating the ages of clades using molecular data from extant organisms and a fragmentary fossil record, and showed how the use of different methods could result in a range of differing results.