Zlil Sela (Hebrew: זליל סלע) is an Israeli mathematician working in the area of geometric group theory.

The machinery of group actions on real trees, developed by Eliyahu Rips, played a key role in Sela's approach.

The solution of the isomorphism problem also relied on the notion of canonical representatives for elements of hyperbolic groups, introduced by Rips and Sela in a joint 1995 paper.

[17][18][19][20] Sela applied a combination of his JSJ-decomposition and real tree techniques to prove that torsion-free word-hyperbolic groups are Hopfian.

Namely, in a long series of papers,[23][24][25][26][27][28][29] he proved that any two non-abelian finitely generated free groups have the same first-order theory.

His work relied on applying his earlier JSJ-decomposition and real tree techniques as well as developing new ideas and machinery of "algebraic geometry" over free groups.