  In this presentation we overview some recent results on biased tracer
diffusion in lattice gases. We consider both models in which the gas particles
density is explicitly conserved and situations in which the lattice gas
particles undergo continuous exchanges with a reservoir, which case is
appropriate, e.g., to adsorbed monolayers in contact with the vapor phase. For
all these models we determine, in some cases exactly and in other ones - using
a certain decoupling approximation, the mean displacement of a tracer particle
(TP) driven by a constant external force in a dynamical background formed by
the lattice gas particles whose transition rates are symmetric. Evaluating the
TP mean displacement explicitly we are able to define the TP mobility, which
allows us to demonstrate that the Einstein relation between the TP mobility and
the diffusivity generally holds, despite the fact that in some cases diffusion
is anomalous. For models treated within the framework of the decoupling
approximation, our analytical results are confirmed by Monte Carlo simulations.
Perturbance of the lattice gas particles distribution due to the presence of a
biased TP and the form of the particle density profiles are also discussed.
