Three classes of problems are considered: 1. minimization of the largest of several ratios, 2. minimization of the sum of ratios, and 3. multiobjective fractional programs. For class 1 duality results as well as an algorithm are presented. For class 2 and 3 algorithmically useful properties of these models are derived. Much of the research has been done in collaboration with J. P. Crouzeix, J. A. Ferland, R. Jagannathan and T. J. Lowe.