Professor Janssen  concentrated his practice in pharmaceutical, medical device, and mass torts defense and risk containment.  In practice, he was involved in various high-profile drug and device cases, including the national diet drug (“fen-phen”) litigations, DES litigations, and myelographic contrast dye litigations.  Both as a practitioner and in academia, he has spoken and written frequently on pharmaceutical and medical device law.

Professor Janssen focuses his scholarship on federal practice and procedure.  He is an author of six national titles in this discipline.  He is the sole author of Federal Civil Procedure Logic Maps (West 3d ed. 2022), a visual learning resource for federal civil procedure, and a co-author of four texts: Practicing Civil Discovery (Carolina 2020), a coursebook for civil discovery simulations; A Student’s Guide to the Federal Rules of Civil Procedure (West, annually, 26th ed. 2023), a rules book and study guide for students; Mastering Multiple Choice – Federal Civil Procedure (West 4th ed. 2022), a multiple choice practice tool; and the Federal Civil Rules Handbook (Thomson Reuters, annually, 30th ed. 2022), a national practitioner resource.  The content of the Handbook is reprinted each year as Volume 12B of the national treatise, Wright & Miller’s Federal Practice and Procedure (Thomson Reuters 2022, annually). 

He is also a contributing author to Rice’s Attorney-Client Privilege in the United States (Thomson Reuters, annually, 2023), a leading treatise on the privilege. His seventh text, a practitioner’s discovery resource for new attorneys, is due to be published soon.

In addition to these books, Professor Janssen is also the author of various journal articles, book chapters, and bar review materials on federal civil procedure, and has lectured widely on civil procedure topics.

Professor Janssen’s scholarship also includes an emphasis on constitutional religious liberty and the Religion Clauses to the United States Constitution, an area of law in which he has written, spoken, and litigated.

While a student at the American University’s Washington College of Law, Professor Janssen was the executive editor of the American University Law Review, a dean’s fellow, a moot court board member, an interschool moot court competitor, and the first-year moot court champion.  After law school, he served as a law clerk to a federal district court judge (Hon. James McGirr Kelly, E.D. Pa.) and to a federal court of appeals judge (Hon. Joseph F. Weis, Jr., 3d Cir.).

Before joining the Charleston School of Law faculty, Professor Janssen taught, while in active practice, as an adjunct instructor at Temple University School of Law for five academic terms and as an adjunct teaching business law at Saint Joseph’s University.