Perl FAQ : Regular Expressions
Pattern matching and regular expressions.

Perl Regular Expression Quick Reference
One-page document containing tabulated summaries of common codes, modifiers, and special characters. [PDF]

How Regexes Work
An article about how to use regular expressions in Perl by M-J Dominus.

Regular Expressions
A description of the patterns used in Perl for pattern matching.

Dirty Secrets of the Perl Regex Engine
Slides from a talk the author presented at TPC and YAPC. Covers the /o flag and re 'eval'.

Perl Regular Expression Matching is NP-Complete
A discussion of the complexity of regular expression matching algorithms in Perl.

MakeRegex
The Perl-module by Hakan Kjellerstrand composes a regex-expression from a list of words.

Perl Regular Expression Tutorial
A tutorial that shows how to use Regular Expressions in Perl.

perlretut
Basic tutorial, distributed as part of the core documentation.

PERL5 Regular Expression Description
Detailed description written by Tom Christiansen in response to a question posted to comp.lang.perl.misc.

Perl Regex
An introduction covering basic concepts.

perl.perl6.language.regex
Archive of discussion relating to regular expressions in Perl 6.

Perldoc.com - perlre
Describes the syntax of regular expressions in Perl.

Perldoc.com - perlretut
A tutorial for regular expressions in Perl.