Rui António Loja Fernandes (July 20, 1965, Coimbra) is a Portuguese mathematician working in the USA.

Fernandes obtained a bachelor's degree in Physics Engineering at Instituto Superior Técnico (Lisbon, Portugal) in 1988.

His PhD thesis was entitled "Completely Integrable bi-Hamiltonian Systems" and has been written under the supervision of Peter J.

[2][3] In 2012 he moved back to the USA and since then he is the Lois M. Lackner Professor of Mathematics at University of Illinois at Urbana–Champaign.

Among his most well-known results are a solution to the long-standing problem of describing the obstructions to the integrability of Lie algebroids[6] and a new geometric proof of Conn's linearization theorem,[7] both written in collaboration with Marius Crainic.