For summer internships, it's often best to apply in the fall. Some programs, such as the State Department, have deadlines as early as November 1. The majority of overseas internship programs are sponsored by universities. These are among the most easily available options for undergraduates, although admission can be competitive. Advantages of these include credit, applicability of financial aid, and a wide variety of subjects and locations available.
Disadvantages are cost and sometimes unpredictability of placement.
Purdue graduate students should consult advisers in their program for official exchanges. A few reciprocal exchange programs offer paying internships in applied fields. All these organizations accept applications directly from students. They recommend that you join a year or so in advance of the desired time for an internship placement, in order to earn points towards the internship, but there are opportunities for non-members as well. As a general rule, the larger and better-known the organization, the more competitive the application process for internships will be.