Interferences are a relatively rare, but nonetheless integral, part of United States patent practice. For many years, patent applicants or patentees who performed their relevant research and development work outside the United States were limited to claiming the dates of their relevant patent applications filed under the Paris Convention, the benefit of which could be claimed pursuant to 35 USC § 119 as the date of conception and reduction to practice of an invention covered in a US patent application or patent held to "interfere" with another US application or patent. Given that such persons may now seek to prove prefiling dates of conception of an invention, or of actual reduction to practice thereof, when the pertinent work was done outside the United States, it has become important for counsellors and in-house advisers of non-US based entities to pay greater attention to interference law, especially as it relates to conception and actual reduction to practice, than they did when their prospective participation in an interference proceeding was hobbled, as noted above.
