The Bank of New York's ADR site

JP Morgan's ADR site

American Depositary Receipts — American Depositary Receipts (ADRs) as an investment; how ADRs are created; how ADRs work; Level I, II, and III sponsorship.

SEC guide to foreign investing for U.S. Citizens (PDF)

ADR.Com - News, earnings estimates, quotes, technical charts, and institutional ownership.

Bank of New York Global Depositary Receipts - Database of all Depositary Receipt programs around the world. Multiple filters to search and analyze DRs by company, country, stock exchange and other criteria.

Citibank American Depositary Receipt Services (ADR) - Information on U.S. investment in non-U.S. securities, particularly via American Depositary Receipts (ADRs).

Deutsche Bank Depositary Receipts Handbook (PDF)

FSA Depositary Receipts - Guide to listing (PDF)