It is "relating to" or "related to"?

In some cases there may be a slight difference between them.

Relating to:"about or concerning."

The less tangible effects of the Senate bill will come from the provisions relating to jobs and social services for immigrants. (LDOCE)

The 1951 Convention relating to the Status of Refugees is the key legal document in defining who is a refugee, their rights and the legal obligations of states. http://www.unhcr.org/pages/49da0e466.html

Related to: connected with

Police say a suspect related to the call for assistance fled the apartment and was located by police. (boston dot com)

cf. reviews of non-technical books relating to Probability http://www.stat.berkeley.edu/~aldous/157/books.html

any good books related to The Hunger Games? http://answers.yahoo.com/question/index?qid=20100626161250AASraxZ

I think the main difference is that if your subject DOES the action so you should use "relating to" but if it RECEIVES the action "related to" must be used.

In addition to the wonderful answers already written above, I dare only claim to offer my 2 cents: Often replacing a phrase with another can be a good way to judge whether something sounds right: Consider replacing "relating to" with "pertaining to" or "in relation to"; they have very similar meanings and are used under very similar conditions (although the former might be slightly weaker than the first of the latter) while replacing "related to" with "has/have/had a relation with"

exempli gratia

1. This book contains a series of short stories relating to her life -> This book contains a series of short stories in relation to her life
2. This article relating to law and order is very comprehensive -> This article in relation to law and order is very comprehensive
3. Is she related to the president? -> Does he have a relation to the president? ("to" and not "with" is used here intentionally, since I don't mean a relationship, does anyone disagree?)
4. This passage is related to the previous one; they share some similarities. -> This passage has a relation/relations to the previous one; they share some similarities.

"Relating to"'s usage seems to be a proper subset of that of "related to" too, (partially because "related to" can denote kinship relations "I am related to her", "I'm somewhat related to her; she's my eighth cousin once removed", these would derive from "relative")

"Relating to" is perhaps more related to the verb "relate" (as in "I relate with your experience"; it's more intimate), while "related to" could derive from "relation". Lastly, perhaps consider "relating to" as a stronger/more emphasized version of "related to"; in example 1 above, the short stories relate to her life and that's why they are included in the anthology, it's not just a side note or coincidental relation.