Why do some courses appear multiple times in the catalog with different section numbers?

The first digit of the three digit section number indicates what week the selective is offered. If it is offered in Week 1 for 1-credit, it will begin with a 1; if it is offered in Week 2 for 1-credit, it will begin with a 2; and if it is offered for both weeks for 2-credits, it will begin with a 3. Please make sure to select the correct section number when registering–this is often true for extramurals and other external experiences. The last two digits of the section number indicate the unique topic number for each selective.