This legendary debate took place at the Graduate School of Design, Harvard University, on November 17th 1982. Not long before it, Alexander had given a talk on The Nature of Order, which was to become the subject of his magnum opus of architecture philosophy. The original version he envisaged was less than half the size of the final four-volume work as it now stands, but its main ideas were already formulated.
Before the debate Eisenman had listened to the tape of Alexander's talk — one of the first public presentations of the ideas in The Nature of Order. What followed was thus partly shaped by the those ideas. What ensued can be said to represent an historic occasion: Alexander is presenting his basis for the New Paradigm in Architecture at the same time as Eisenman presents his competing, diametrically opposed, deconstrutivist claim for such a Paradigm.
The importance of the debate has been widely recognised. Twenty years later, the Harvard Graduate School of Design republished it alongside three other seminal documents from the post-1969 period: an early piece by Alexander Tzonis on the "end of ideology in architecture", and a recent debate on urbanism between Rem Koolhaas and Andres Duany. Some people may only have heard of the 1982 encounter because Alexander said Eisenman was "fucking up the world" in a public forum; but if this is all one knows about it, one is not prepared for the generally good-natured tone of most of the exchanges.
Source and more: Katarxis