In 1995, Selberg lectured on arithmeticity at ETH in Zurich. The original transparencies for this talk, along with a xerox copy of some transparencies used in a very similar one, turned up at home in a folder labelled "1963".
When Selberg had need of these transparencies in 2003, he was unable to locate them. He asked Chandrasekharan at ETH to make a copy of the xerox copy that Selberg had sent him back in 1995. Files 1 and 2 below correspond to the ETH talk; file 3 to the related one. The work described in these lectures dates back to the early 1960s and early 70s; it has a very close link to item #35 in the list of publications.
The last 7 files, S1--S7 [added June 2013], are some additional lecture fragments and preparations taken from the relevant folders. The first four of these make reference to the L-function connection cited in section 7.5 of item #35.