It is a corner stone of every modern US Presidential election – the debate.

Held late in the election cycle after the political parties have nominated their candidates, they usually meet in a large hall, often at a university, before an audience.

The formats of the debates have varied, with questions sometimes posed from one or more journalist moderators and in other cases members of the audience.

Viewing figures

Broadcast live on television and radio, the first debate for the 1960 election drew over 66 million viewers out of a population of 179 million making it one of the most-watched broadcasts in U.S. television history.

The 1980 debates drew 80 million viewers out of a 226 million.

Recent debates have drawn decidedly smaller audiences – ranging from 46 million for the first 2000 debate to a high of over 67 million for the first debate in 2012.

In Video

Coming up are highlights of the 2012 debates between Obama & Romney, as well as the Vice-Presidential debate.

But first CNN looks back at the highs and lows of what can be an election decider:

First Presidential debate highlights:

Second Presidential debate highlights: US Vice Presidential debate highlights: Final Presidential debate highlights: