Klainerman, Sergiu, Uniform decay estimates and the Lorentz invariance of the classical wave equation. Communications on Pure and Applied Mathematics, vol. 38 (1985), no. 3, pp. 321–332
Klainerman, Sergiu, The null condition and global existence to nonlinear wave equations. Nonlinear systems of partial differential equations in applied mathematics, Part 1 (Santa Fe, N.M., 1984), pp. 293–326, Lectures in Appl. Math., 23, American Mathematical Society, Providence, RI, 1986. ISBN0-8218-1125-80-8218-1125-8
Klainerman, Sergiu; Machedon, Matei, Space-time estimates for null forms and the local existence theorem, Communications on Pure and Applied Mathematics, vol. 46 (1993), no. 9, pp. 1221–1268
Christodoulou, Demetrios; Klainerman, Sergiu, The global nonlinear stability of the Minkowski space. Princeton Mathematical Series, 41. Princeton University Press, Princeton, NJ, 1993. ISBN0-691-08777-60-691-08777-6
Klainerman, Sergiu; Machedon, Matei, Smoothing estimates for null forms and applications. A celebration of John F. Nash, Jr., Duke Mathematical Journal., vol. 81 (1995), no. 1, pp. 99–133