String theory is a typical interdisciplinary subject, bringing together ideas, techniques and intuition from both physics and mathematics. As such it is a prime example of mathematical physics in the broad sense of the word. The Netherlands play a prominent part in the international developments, as witnessed by the coming organisation of Strings '97 in Amsterdam, that will also be supported by the Stieltjes Institute. These activities are spread over several research schools; in particular our mathematical physics group works closely together with the groups of H. Verlinde and E. Verlinde at the Theoretical Physics Institutes of the Universities of Amsterdam and Utrecht respectively. There are also various collaborations in the mathematical community, in particular in the SWON project Riemann surfaces and algebraic curves. Within the Stieltjes Institute the relations with algebraic geometry are more central. This good infrastructure must form a solid basis to further develop the activities in this exciting field.