MOM is continually being infused with new ideas and the resulting growth can present problems. For example, anyone who repeatedly changes or adds to a large model will appreciate that after time, the model can become unmanageable. At some point, inter-connectivity between sections of code increases to a point where making changes in one place inadvertently breaks something seemingly unrelated. Further limitations become apparent when previously added code acts as a road block to new development. To a large extent, modularity has been used as the key organizational approach to solve this problem and its use is explained in Chapter 15. The other part of the solution involves resisting temptation to make changes in a quick and dirty way for short term gains which inevitably turn into long term hindrances. Again, Fortran 90 with its well defined modules and interfaces should increase modularity.