  Galaxy redshift surveys are a major tool to address the most challenging
cosmological problems facing cosmology, like the nature of dark energy and
properties dark matter. The same observations are useful for a much larger
variety of scientific applications, from the study of small bodies in the solar
system, to properties of tidal streams in the Milky Way halo, to galaxy
formation and evolution. Here I briefly discuss what is a redshift survey and
how it can be used to attack astrophysical and cosmological problems. I finish
with a brief description of a new survey, the Javalambre Physics of the
Accelerating Universe Astrophysical Survey (JPAS), which will use an innovative
system of 56 filters to map ~8000 square degrees on the sky. JPAS photometric
system, besides providing accurate photometric redshifts useful for
cosmological parameter estimation, will deliver a low-resolution spectrum at
each pixel on the sky, allowing for the first time an almost all-sky IFU
science.
