The high-redshift galaxies became a distinct research ?eld during the
?nal decade of the20thcentury.
AtthattimetheLyman-breaktechniquemadeitpossibletoidentify signi?cant
samples of such objects, and the new generation of 8 to 10-m telescopes
resulted in ?rst good spectroscopic data. Today the high-redshift
galaxies have developed into one of the important topics of
astrophysics, accounting for about 5-10% of the publications in the
major scienti?c journals devoted to astronomy. Because high-redshift
galaxies is a rapidly developing ?eld and since new results are
published constantly, writing a book on this topic is challenging. On
the other hand, in view of the large amount of individual results now in
the literature, and in view of the still growing interest in this topic,
it appears worthwhile to summarize and evaluate the available data and
to provide an introduction for those who wish to enter this ?eld, or
who, for various reasons, might be interested in its results. The end of
the ?rst decade of the 21st century appears to be a good point in time
to attempt such a summary. The current generation of ground-based 8 to
10-m - optical telescopes, the Hubble Space Telescope, and the most
important large radio telescopes have by now been in operation since
about one or two decades. Although these instruments will continue to
produce important scienti?c results for some time to come, many of the
initial programs exploiting their unique new possibilities have been
completed.