Reference for Nori motives

Probably the best introduction has already been mentioned by Donu Arapura, and it is available online:

• Marc Levine, Mixed Motives (2005)

Section 1 ("Essentials of Nori Motives") of this paper might also be useful:

• Annette Huber & Stefan Müller-Stach, On the relation between Nori Motives and Kontsevich Periods (2011)

Also, there are some interesting unpublished notes on motives by Nori himself:

• Madhav Nori, Lectures at TIFR

There are brief outlines in various places, such as an article by Marc Levine on motives in the K-theory handbook. However, the most complete reference is the manuscript "Periods and Nori motives" by Annette Huber and Stefan Müller-Stach. I expect that it will be published in the near future. In the meantime, I suspect a copy may be available from one of their web pages, or perhaps you need to ask them.

The PhD thesis of D. Harrer is now available on Arxiv.

https://arxiv.org/ftp/arxiv/papers/1609/1609.05516.pdf