A linear dependent source is a dependent voltage or current source whose output voltage or current is proportional only to the first power of some voltage or current variable in the circuit or a linear combination (the sum or difference of such variables). For example, v _xy = 2v ₁ ? 3i ₂ is a linear relationship but p = vi = Ri ² = v ²/R and i = I _Se ^{v/nV _T} are non-linear.

A linear circuit is a circuit which is composed entirely of independent sources, linear dependent sources and linear passive elements or a combination of these.