Hi there. My husband and I are visiting St. Martin in July but first we are stopping in Puerto Rico for a few days on the way there. This will be the first time that both of us will be traveling outside of the U.S. and we are a little confused about the whole process of going through customs. We are flying out of San Francisco and arriving in Puerto Rico (San Juan) and we are aware that we do not need to go through customs at this point because Puerto Rico is technically part of the U.S. and we are U.S. citizens. After leaving Puerto Rico we will arrive at St. Martin's and we are aware that now we will have to go through customs. However, the confusion begins here. At the end of our trip we will leave St. Martin, head BACK to San Juan as part of the layover, then Miami and then San Franciso. At what point do we go back through customs? Do we go in St. Martin and then also in Puerto Rico, or just St. Martin? Also, what is the process of going through customs? What other information do you need other than passports? And finally, do we go through both customs AND immigration or just customs? If someone with experience could please clear up our confusion and explain this process to us we would greatly appreciate it! Thanks! Also, sorry for the long post!