<p>Methane pyrolysis by thermal plasma has been investigated for more than three decades as a promising route to produce CO₂-free hydrogen together with valuable carbon materials. This article is based on the plenary lecture delivered at the 26th International Symposium on Plasma Chemistry (ISPC-26, June 2023, Minneapolis) and distills the key scientific and technological advances achieved since the early 1990s. Topics include fundamentals of arc physics and thermodynamics, diagnostics and modeling of plasma–molecule interactions, and reactor engineering from laboratory to pilot scale. The extreme temperatures and rapid quench achievable in thermal plasmas enable fast CH₄ conversion and reveal radical-driven pathways for aromatic growth, particle nucleation, and carbon morphology control. Progress in arc stabilization, energy coupling, and residence-time management has improved conversion, selectivity, and carbon quality, while offering clearer scale-up criteria. Recent demonstrations indicate the onset of an industrial transition, targeting low-carbon hydrogen and engineered carbon (e.g. carbon black, nanotubes, nanofibers, graphene flakes…). We outline remaining challenges - plasma source efficiency, reliability, electrode lifetime, transport and mixing at scale, and standardized product characterization - and identify opportunities for process intensification and integration with renewables. By bridging fundamental plasma chemistry with applied reactor design, thermal-plasma methane pyrolysis emerges as a credible pathway to decarbonize hydrogen production and to manufacture high-value carbon materials.</p>