The license you choose defines the social contract you wish to set up
among your co-developers and users. The copyright you put on the software
will function mainly as a legal assertion of your right to set license
terms on the software and derivative works of the software.
Anything that is not public domain has a copyright, possibly more than
one. Under the Berne Convention (which has been U.S. law since 1978),
the copyright does not have to be explicit. That is, the authors of a
work hold copyright even if there is no copyright notice.
Who counts as an author can be very complicated, especially for
software that has been worked on by many hands. This is why licenses
are important. By setting out the terms under which material can be
used, they grant rights to the users that protect them from arbitrary
actions by the copyright holders.
In proprietary software, the license terms are designed to
protect the copyright. They're a way of granting a few rights to
users while reserving as much legal territory is possible for the
owner (the copyright holder). The copyright holder is very important,
and the license logic so restrictive that the exact technicalities of
the license terms are usually unimportant.
In open-source software, the situation is usually the exact opposite;
the copyright exists to protect the license. The only rights the
copyright holder always keeps are to enforce the license. Otherwise,
only a few rights are reserved and most choices pass to the user. In
particular, the copyright holder cannot change the terms on a copy you
already have. Therefore, in open-source software the copyright holder
is almost irrelevant -- but the license terms are very important.
Normally the copyright holder of a project is the current
project leader or sponsoring organization. Transfer of the project to
a new leader is often signaled by changing the copyright holder.
However, this is not a hard and fast rule; many open-source projects
have multiple copyright holders, and there is no instance on record of
this leading to legal problems.
Some projects choose to assign copyright to the Free Software Foundation,
on the theory that it has an interest in defending open source and lawyers
available to do it.
For licensing purposes, we can distinguish several different
kinds of rights that a license may convey. Rights to copy
and redistribute, rights to use,
rights to modify for personal use, and rights to
redistribute modified copies. A license may
restrict or attach conditions to any of these rights.
The Open Source
Initiative is the result of a great deal of thought about what
makes software ``open source'' or (in older terminology) ``free''.
Its constraints on licensing require that:
An unlimited right to copy be granted.
An unlimited right to use be granted.
An unlimited right to modify for personal use be granted.
The guidelines prohibit restrictions on redistribution of
modified binaries; this meets the needs of software distributors, who
need to be able to ship working code without encumbrance. It allows
authors to require that modified sources be redistributed as pristine
sources plus patches, thus establishing the author's intentions and an
``audit trail'' of any changes by others.
The OSD is the legal definition of the `OSI Certified Open Source'
certification mark, and as good a definition of ``free software'' as
anyone has ever come up with. All of the standard licenses (MIT, BSD,
Artistic, and GPL/LGPL) meet it (though some, like GPL, have other
restrictions which you should understand before choosing it).
Note that licenses which allow noncommercial use only do
not qualify as open-source licenses, even if they
are decorated with ``GPL'' or some other standard license. They
discriminate against particular occupations, persons, and groups.
They make life too complicated for CD-ROM distributors and others
trying to spread open-source software commercially.
Take our 
