12-bar blues structure

Concept

The 12-bar blues is a 12-measure form using only I, IV, V. The standard layout: I-I-I-I / IV-IV-I-I / V-IV-I-V. With 7th chords (E7-A7-B7 in E blues) it becomes pure blues. Every blues, rock-and-roll, and early R&B song uses some flavor of this.