Redaction Criticism is a discipline which studies both the way the redactors/editors/authors changed their sources and the seams or transitions they utilized to link those transitions into a unified whole. The purpose of this approach is to recover the author's theology and setting. Unlike 'Literary Criticism' which looks at the individual gospels as a literary whole and cares little about authorial intent, Redaction Criticism wants to ask questions like, 'What is the specific theological emphasis in Luke, or why does Matthew change the order of his account to Mark. Of Course, when Matthew, Mark and Luke are talked about what is meant is an unknown author (or more likely) authors, editors are redactors who put that particular document together.
The 'Q' Hypothesis: Q is from the German 'Quelle' (source) and is a hypothetical document that contains the 230 so sayings of Jesus which Matthew and Luke share, but which are not found in Mark (thus the basis of the 'Synoptic Problem'). It is claimed that Matthew and Luke had drawn on two main sources to compile their own gospels: Mark's gospel and a collection of sayingsof Jesus referred to as 'Quelle' by German critics. It was J.Weiss in 1890 who shortened it to Q.
As an overall great resource on this you should get a hold of:
'Dictionary of Jesus and the Gospels' edited by Joel Green, Scot McKnight and I. Howard Marshall. It's an IVP publication and has many good conservative writers.
'Exploring the New Testament Vol 1: The Gospels and Acts' by David Wenham and Steve Walton is another great resource.
Although it is less conservative I was assigned:
'The Gospels and Jesus' (2nd Edition) by Graham Stanton. It covers the material well and lays out what you need to know.
Other books that are helpful particularly regarding Redaction Criticism and Q:
'The Gospels for all Christians' by Richard Bauckham
'The Synoptic Problem' by Robert Stein
'Reading Matthew, Mark and Luke: A Fresh Assault on the Synoptic Problem' by J.W. Wenham
Websites:
The New Testament Gateway | NTGateway.com | Dr Mark Goodacre is the website of Mark Goodacre who is a modern critic of Q.
www.biblicaltraining,org is the website of William Mounce and if you register you can download Robert Stein's Mp3s on these and other subjects.