Per H. Enflo (Swedish: [ˌpæːɹ ˈeːnfluː]; born 1944) is a mathematician who has solved fundamental problems in functional analysis. Three of these problems had been open for more than forty years.
The basis problem and the approximation problem and later the invariant subspace problem for Banach spaces. In solving these problems, Enflo developed new techniques which were then used by other researchers in functional analysis and operator theory for years. Some of Enflo's research has been important also in other mathematical fields, such as number theory, and in computer science, especially computer algebra and approximation algorithms. Enflo works at Kent State University, where he holds the title of University Professor. Enflo has earlier held positions at the University of California, Berkeley, Stanford University, École Polytechnique, (Paris) and The Royal Institute of Technology, Stockholm. Enflo is also a concert pianist.