How does the 12-bar blues chord progression use the I, IV, and V chords?

The 12-bar blues is a foundational chord progression in blues music that organizes the tonic (I), subdominant (IV), and dominant (V) chords into a repeating 12-measure structure. This framework provides a predictable harmonic foundation while allowing for expressive improvisation.12

The progression is typically divided into three four-bar phrases as follows:

• Phrase 1 (Measures 1–4): The I chord is played throughout these four bars, establishing the home key.12
• Phrase 2 (Measures 5–8): This phrase begins with two bars of the IV chord, followed by two bars returning to the I chord.12
• Phrase 3 (Measures 9–12): The final phrase creates harmonic tension and resolution, typically consisting of one bar of the V chord, one bar of the IV chord, and two bars of the I chord (often concluding with a "turnaround" that may lead back to the V chord).12

This structure relies on the functional relationship between these chords to create a sense of movement, tension, and release that is characteristic of the genre.1