Linq, this is Relational Data. Relational Data, this is Linq... Introducing LINQ to Relational Data Whitepaper

MSDN .Net Framework Development Center - Introducing LINQ to Relational Data

"This article introduces two implementations of LINQ, LINQ to SQL and LINQ to Entities, and the key scenarios for which each was designed. (19 printed pages)

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What is Linq to SQL? How's that different from Linq to Entities? When should you use which? What's the benefit of one over the other?

Those are some of the questions this somewhat high level (level 100/200) whitepaper tries to help with...

(via Kirk Allen Evans's Blog - LINQ to SQL vs. LINQ to Entities Smackdown!)