It's most often attributed to Albert Einstein, sometimes to Benjamin Franklin, but I have never seen a specific citation for either one, which makes me suspect it was neither.

It doesn't sound like Franklin to me. (Is "over and over" a phrase that was used in the 18th century? It sounds more modern than that -- I think Franklin would more likely have said "repeatedly.")

I suspect this one really should be attributed to the prolific "Anonymous."

First, I wrote, "Albert Einstein.", and hit the submit button. About thirty seconds later, I discovered the author was Ben Franklin. And then I found out editing answers had just become impossible, Furthermore, things would be like that for a while.

There's nothing like staring at the absence of "edit this answer" to make you wish the federal government was spending billions of dollars on time travel instead of arrogance. Or, more realistically, to make me wish I'd verified the information before answering. Thanks to Bob for being so cool about the whole thing. Very decent of you, considering my answer was wrong and stayed that way for a while. Live and learn:)

Benjamin Franklin who died in 1790 is credited with this quote about insanity.
"The definition of insanity is doing the same thing over and over and expecting a different result."

"Insanity is doing the same thing over and over again and expecting different results.
This and variations on it have been attributed to various different sources, including Benjamin Franklin, Albert Einstein, an old Chinese proverb, and Rita Mae Brown"
Source:
http://en.wikiquote.org/wiki/Insanity

“One definition of insanity is to do the same thing, day-after-day, expecting different results”
- Mark Silber

“The very definition of insanity is to keep doing the same thing over and over again, expecting different results.” - Philip Mangano

“Insanity is doing the same thing in the same way and
expecting a different outcome”

Old Chinese Proverb

http://en.thinkexist.com/search/searchquotation.asp

http://www.brainyquote.com/.../...rteins133991.html

http://www.saidwhat.co.uk/.../...ty_is_doing_13716

I think it was Einstein

Actually it stems from Rita Mae Brown's novel Sudden Death, New York , 1983, p. 68.

I am a chinese. I have very good knowledge on chinese proverb. I have never hear this. so this isn't chinese proverb I think.

None of the answers so far answer the question. Who first said or wrote that definition of insanity? It has become quite popular, and I'd not realized it was so muddled in attribution-land. In checking the Net I've seen a perfect example of the squirriliness of Net sources, with Net authorities stating with equal assuredness that it was Einstein, Ben Franklin, and at least two others including "ancient Chinese proverb." I seriously doubt each one, but that means I could be wrong at least one out of four or five times. Franklin didn't speak or write in such terms (He would have said "madness" and "repeatedly" and inserted a "ye" or a "whereas" here and there, methinks).
I'd keep trying on the Net, but I'm beginning to think one of you out there might take on a big assignment and look it up in some paper, volume, periodical and otherwise obsolete "library" institution. Meanwhile I'll go on about my life. Good luck!

i would say one of the 5 or so people listed above, and to further add to it, this sounds like a form of insanity i could live with!