  This thesis deals with different aspects of a special kind of high redshift
galaxy, namely Ly-alpha emitters. Ly-alpha emitters are galaxies found through
their Ly-alpha emission, at redshifts larger than z >~ 2 where the emission
line has been redshifted into the optical or near-infrared regime. The thesis
has two main parts; a lower redshift, observational part (z ~ 3) and a more
technical/theoretical very high redshift part (z ~ 9).
  In the first, lower redshift part I present the analysis of a narrow-band
image taken in the GOODS-S field, focused on a redshift for Ly-alpha of z =
3.15. The image, covering a central part of the GOODS-S field revealed 25
Ly-alpha emitting candidates, of which one turned out to be a so-called
Ly-alpha blob. In the second part, I discuss future, very high redshift
narrow-band surveys for Ly-alpha emitters. Finally, in a project unrelated to
the other two parts of the thesis, I present a search for a 'Fundamental plane'
of Ly-alpha emitters in the colour space produced by large-scale
multi-wavelength surveys such as GOODS or COSMOS. [Abridged]
