Object orientated history

i am starting now to see how many excellent new ways of doing things the Object orientated approach is giving me, i am going through old stuff and trying to rework it with the OO approach, i am just wondering how long this has been around for? i know about C++ as widely recognised OO language but when was the concept first experimented with? were there other languages that used it before then? was it just a conceptual leap that led to programs built in this way or was it that the concept had been widely discussed before but the technology did not allow for it to be used? I can imagine programmers in the past picturing a language that supported the OO features but that was not available at the time.

You can find a quick rundown of OOP history here.