  Information is central to thermodynamics, providing the grounds to the
formulation of the theory in powerful abstract statistical terms. One must not
forget, however, that, as put by Landauer, {\it information is physical}. This
means that the processing of information will be unavoidably linked to the
costs of manipulating the real physical systems carrying the information. Here
we will focus on the particular process of erasing information, which plays a
fundamental role in the description of heat engines. We will review Landauer's
principle and the associated erasure energy cost. We will also show, following
the recent contributions from Vaccaro and Barnett, that cost of erasing does
not need to be paid with energy, but with any other conserved quantity.
Finally, we will address the issue of designing heat engines based on these new
concepts.
