A salient feature of solid-state quantum-Hall-type topological materials in two dimensions is the presence of conducting electronic edge states that are insensitive to scattering by disorder. Such unidirectional edge states have been predicted and observed in many other experimental settings, including photonics, mechanical, and acoustic structures. It is of great interest to understand how topological states behave in the presence of interparticle interactions and nonlinearity. Here, we experimentally demonstrate backscatter-immune unidirectional solitonlike nonlinear states on the edge of photonic topological insulators consisting of laser-written waveguides. As a result of the optical Kerr nonlinearity of the ambient glass, the solitonlike wave packet forms a long-lived quasilocalized coherent structure that slowly radiates power into the bulk and along the edge. The realization of solitonlike edge states paves the way to an understanding of nonlinear and interacting topological systems.2 MoreReceived 4 May 2021Revised 18 October 2021Accepted 21 October 2021DOI:https://doi.org/10.1103/PhysRevX.11.041057Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasKerr effectOptical solitonsPhotonicsTopological effects in photonic systemsTopological materialsAtomic, Molecular & OpticalCondensed Matter, Materials & Applied PhysicsNonlinear Dynamics