The SAGEX review on scattering amplitudes by Travaglini, G, Brandhuber, A, Dorey, P, McLoughlin, T, Abreu, S, Bern, Z, Bjerrum-Bohr, NEJ, Blümlein, J, Britto, R, Carrasco, JJM, Chicherin, D, Chiodaroli, M, Damgaard, PH, Del Duca, V, Dixon, LJ, Dorigoni, D, Duhr, C, Geyer, Y, Green, MB, Herrmann, E, Heslop, P, Johansson, H, Korchemsky, GP, Kosower, DA, Mason, L, Monteiro, R, O’Connell, D, Papathanasiou, G, Planté, L, Plefka, J, Puhm, A, Raclariu, A-M, Roiban, R, Schneider, C, Trnka, J, Vanhove, P, Wen, C, White, CD