This is the introductory paper by R. Milner on pi-calculus:
http://www.lfcs.inf.ed.ac.uk/reports/89/ECS-LFCS-89-85

The page has also a link to the companion paper which goes deeper into theory.

-- ZeljkoVrba

I was hoping to find a nice, easy intro to this here, but alas not. All I've got so far is this:

http://www-ics.ee.ic.ac.uk/~frank/surp98/report/gdj1/pi-calculus.html

and a pdf of a paper on the Polyadic Pi calculus, but it looks a bit heavy going... 

-- DannyAyers

''I highly recommend RobinMilner's book, "Communicating and Mobile Systems: the Pi-Calculus", ISBN 0521658691.''

-- DaveHerman

Thanks - it's certainly well written, though the maths is pretty hard. ''I just came across this page again while searching for a link for the book as the joint-scariest on my bookshelf, alongside DougLea's "Concurrent Programming in Java"''

-- DannyAyers

Wikipedia entry: http://en.wikipedia.org/wiki/Pi-calculus

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Comparable to the LambdaCalculus but where that is based on Functions, PiCalculus is based on Processes and arose from modelling Mobile systems. Many strange connectives, example: 
   
  /\/-> (like a crooked arrow) 
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It can be used to specify languages similar to how LambdaCalculus is used in DenotationalSemantics - example with PrologLanguage:

http://scholar.google.com/scholar?cluster=6035347962773538537
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A DenotationalSemantics of PiCalculus itself is given in http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.23.1179. 

A programming language based on it is PictLanguage.
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An example of the DiningPhilosophers Problem in Nomadic Pict:
http://www.cs.put.poznan.pl/pawelw/npict/Philosophers/hall.pi
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See also: JoinCalculus, ModelsOfComputation.

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CategoryConcurrency