Eleny-Nicoleta Ionel is a Romanian mathematician, interested in symplectic geometry and Gromov–Witten invariants. She is a professor of mathematics at Stanford University, where she is chair of the mathematics department.
Ionel is the daughter of Adrian Ionel, a professor at the Ion Ionescu de la Brad University of Agricultural Sciences and Veterinary Medicine of Iași. She earned a bachelor's degree from Alexandru Ioan Cuza University in Romania in 1991, and completed her Ph.D. in 1996 from Michigan State University. Her dissertation, Genus One Enumerative Invariants in , was supervised by Thomas H. Parker. After postdoctoral research at the Mathematical Sciences Research Institute in Berkeley, California and a position as C. L. E. Moore instructor at the Massachusetts Institute of Technology, she joined the University of Wisconsin–Madison faculty in 1998, and moved to Stanford in 2004.