This revision could not have been completed without the help of many people, most important among them is my dedicated and able co-worker, Petra Malesevich, who participated in nearly every phase of the work. I could count on her to continue the research unabated during my long field trips. Along with Bob Magill, she revised, updated and improved the more powerful description program that we used for the Philodendron revision. Joann Beiser, working as an assistant, played an important role for nearly two years, providing help in the preparation of descriptions. Kathy Pickett Upton, Research Greenhouse manager, played a major role in maintaining the live collections, making pollinations and in dealing with label problems. Very special thanks also go to my colleague and fellow aroid specialist Mike Grayum, whose knowledge of the Costa Rican Araceae is without parallel. He has not only made many of the best collections of Philodendron, but his breadth of experience in that part of Central America and his vivid insights into the interrelationships of species were very rewarding. In addition, his skills as an editor and his knowledge of Latin and rules of nomenclature contributed much to this work. Simon Mayo, like Mike Grayum, conducted extensive work on Philodendron. Their work was concurrent or preceded my own and their ideas and interpretations of phenomena in the genus were ever insightful. My own work has benefitted greatly from their work. Dan Nicolson was always generous with his time in helping to solve nomenclatural problems as well as problems with translations of difficult Latin phraseology. Gordon McPherson provided pickled material of many species of Philodendron during his tenure as our resident botanist in Panama. Eleanor Sauer has proofread or written Latin diagnoses for nearly all of the new species. Dr. Joseph Tosi, of the Tropical Science Center in San Jose, Costa Rica assisted us in standardizing our use of the Holdridge Lifezone System that we have added to our computerized database. Leland Russell, summer volunteer and later summer employee while on summer break from his undergraduate studies at Carleton College in Minnesota made critical comparative studies of Philodendron inflorescences for the Central American species of Philodendron. Finally, I would like to thank my wife Patricia, who has without complaint, allowed me to spend several months each year wandering the tropics of Central and South America for almost three decades. She was always available to solve every computer glitch and has also helped with the computerized sorts of information which led to the construction of the keys.