How to do case insensitive search in Vim

As well as the suggestions for \c and ignorecase, I find the smartcase very useful. If you search for something containing uppercase characters, it will do a case sensitive search; if you search for something purely lowercase, it will do a case insensitive search. You can use \c and \C to override this:

:set ignorecase
:set smartcase
/copyright      " Case insensitive
/Copyright      " Case sensitive
/copyright\C    " Case sensitive
/Copyright\c    " Case insensitive

See:

:help /\c
:help /\C
:help 'smartcase'

You can use the \c escape sequence anywhere in the pattern. For example:

/\ccopyright or /copyright\c or even /copyri\cght

To do the inverse (case sensitive matching), use \C (capital C) instead.