  Galaxy redshift surveys are outstanding tools for observational cosmology.
Mapping the universe as outlined by galaxies leads to fundamental measurements
which refine our knowledge of its structure and evolution. Redshift acquisition
has undergone tremendous progress thanks to advances in technology, and
redshift surveys appear nowadays as routine. Even though they may look simple
at face-value, the strategy of a survey and the galaxy-selection criteria have
crucial impacts on the interpretation of results. In this lecture, I
concentrate on the galaxy luminosity function and its evolution. In particular
I consider the luminosity function derived from optically magnitude-selected
field galaxy redshift surveys. The aim is to describe the approach to designing
state-of-the-art of galaxy surveys and their impact on measurements on
luminosity functions. I start by discussing survey strategies, (Section 2). I
continue by describing the data required (Section 3), and then review the
different estimators to measure luminosity funtions (Section 4). I discuss the
luminosity function evolution (Section 5) and I follow by summarizing the
status of luminosity measurements (Section 6).
