No it doesn't. edit - well, depends on what you mean by "series", but it has nothing to do with the next chord in the 'progression' Yes it is, or at least it stands for a chord. Say that you have a tune that is in the key of A. Your chord I is A. That's the 'home' chord, the place of resolution for the song. We do indeed count up the scale to derive what chords get which numerical designation, so sticking to IV & V.. A = I B = ii C# = iii D = IV E = V F# = vi G# = viidim Yes? So chord IV is D, & chord V is E. These are just names and have no relation whatsoever to the order in which we will play them in the song. Our song might have an intro such as this one: E /// D /// A /// A / E / ...before going on to a standard 12-bar verse pattern. We'd write that intro down as: V /// IV /// I /// I / V / That is the song's chord progression, written either as actual chord names, or roman numerals. We might say that the song has a 'simple I, IV, V progression', because those three chords are all that the song contains, but that's just a description : that doesn't tell us the order to play the chords in, or for how long. Well, we use the roman numerals so that we can change the key of the song, so yes - you're right about that part. If we wanted to play that intro I wrote out in the key of E, we'd work out that I, IV, & V in E are E, A & B, and then plug them into the progression to get... B /// A /// E /// E/B/ But 'a I, IV, V progression' can be anything that just uses those three chords. All of the following could be described as a 'I, IV, V': I /// I /// IV /// V /// I /// IV /// I /// V /// or I /// IV /// I /// V /// or I /// IV /// I /// I /// IV /// IV /// I /// I /// V /// IV /// I /// IV/V/ or V /// IV /// I /// I /// etc Any clearer?