The most important parts of any song are the chorus and the intro. Whilst the importance of a killer chorus is unquestionable, without a compelling, striking introduction, many listeners aren't going to stick with the song long enough to reach the hook.
The ability to construct an instantly memorable opening statement is a gift that some bands seem to possess in spades - the likes of AC/DC and Led Zeppelin have a whole catalogue of attention grabbers, often based on the simplest of riffs.
What all of the entries on this list of '70s classics have in common is that they manage to convey everything you ever need to know about the essence of the band, the song and their attitude in a musical statement lasting less than a minute.
Other decades have their fare share of notable intros, but the music of the '70s seems to have its own unique organic feel and with the dawn of the glam and punk eras, two significant musical movements in one decade that influenced music in general forever afterwards.
Lifelong music obsessive, regular contributor to US guitar magazines, sometime radio presenter, singer/guitarist in Star Studded Sham, true believer in the power of rock'n'roll and an amp turned up to 11.