A colleague of mine is interested in the formal basis of concurrent programming, so I decided to gather several resources and post them here. I should start by saying much that much of the research in concurrent programming is based on the theory of pi-calculus.

• Structured Concurrent Programming - Slides in PDF format from a lecture by Tony Hoare.
• PiLib: A Hosted Language for Pi-Calculus Style Concurrency - An article about the implementation of the pi-calculus as library using the Scala programming language.
• The Polyadic pi-Calculus: a Tutorial (1991)  Robin Milner - An article which provides an introduction and extension to the pi-calculus.
• A Foundation for Actor Computation (1998) Agha et al - An article about the actor model of concurrent computation.
• Multicore programming with Transactional Memory - An article introducing the topic of transactional memory for dealing with concurrency.
• Discussion of the Singularity project at Microsoft - A summary, discussion, and link to the Singularity project at Microsoft to design a safe concurrent operating system.  

Hopefully this provides a few useful and interesting entry points into the study of concurrency in computer science.