2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/55249We review brane engineering of mirror pairs of 3d N=4 theories. It reveals aspects of 3d physics not known from previous field theoretic studies: novel QFT's without Lagrangian description and transitions to them from conventional QFT's.Talk presented at NATO/ASI on Strings, Branes and Dualities, Cargese, 1997. 15 pages, 10 figures, latex 2.09, epsfig, crckapb.styHigh Energy Physics - Theorytext