E. M. Friedlander, 1982, Étale homotopy of simplicial schemes , volume 104 of Annals of Mathematics Studies , Princeton University Press, Princeton, N.J.

E. M. Friedlander, Fibrations in étale homotopy theory (numdam), Publ. Math. Inst. des Haut. Études Scient., 42, (1973), 5 – 46.

Aldridge Bousfield, Eric Friedlander, Homotopy theory of $\Gamma$-spaces, spectra, and bisimplicial sets, Springer Lecture Notes in Math., Vol. 658, Springer, Berlin, 1978, pp. 80-130. (pdf, pdf)