Why Bother With Foreign Patents?

Dear Rich: Why would you bother getting a patent in other countries if you have been granted one in the USA. Surely, if a patent were granted in the USA that would be enough to deter someone from taking it out in other countries? If you had taken out a PCT and filed for the patent in other countries but only taken it to full patent in the USA someone else would surely be prevented from taking a patent out on your idea in the other countries as it had already been published. Is this correct thinking or am I missing something here?  It's true that after you file your patent application, inventors outside the U.S. may be blocked from getting a similar patent in their respective countries. But the lack of foreign patent rights makes it easier to make and sell your invention abroad. After all, if nobody has a patent, anybody can make the invention. (As you're aware, a U.S. patent is only enforced within national borders.) For many inventors, control over the U.S. market is enough -- after all, the U.S. often accounts for one-third or one-quarter of a new product's sales. Also, the cost of obtaining foreign patents can be prohibitive and often outweighs their speculative value. But for big multinationals with global product introductions, international patent protection is necessary.