In algebra, a differential graded Lie algebra, or dg Lie algebra, is a graded vector space L = \bigoplus L_i over a field of characteristic zero together with a bilinear map [,]: L_i \otimes L_j \to L_{i+j} and a differential d: L_i \to L_{i-1} satisfying

[x,y] = (-1)^{|x||y|+1}[y,x],

(-1)^{|x||z|}[x,[y,z]] +(-1)^{|y||x|}[y,[z,x]] +(-1)^{|z||y|}[z,[x,y]] = 0,

d [x,y] = [d x,y] + (-1)^{|x|}[x, d y]

for any homogeneous elements x, y and z in L.

The main application is to the deformation theory in the "characteristic zero" (in particular over the complex numbers.) The idea goes back to Quillen's work on rational homotopy theory. One way to formulate this thesis might be (due to Drinfeld, Feigin, Deligne, Kontsevich, et al.):[1]

Any reasonable formal deformation problem in characteristic zero can be described by Maurer–Cartan elements of an appropriate dg Lie algebra.