Browning himself described this poem as a "dramatic lyric" – at least, Dramatic Lyrics was the title he gave to the book of poems in which "My Last Duchess" first appeared. The "dramatic" part of the poem is obvious: it has fictional characters who act out a scene.
The "lyric" part is less clear. "My Last Duchess" doesn’t read like a typical lyric poem. Its rhymed iambic pentameter lines, like its dramatic setup, remind us of Shakespeare’s plays and other Elizabethan drama. But it is about the inner thoughts of an individual speaker, instead of a dialogue between more than one person. That makes it more like the Romantic lyrics that came before it in the early part of the nineteenth century – stuff by Wordsworth, Coleridge, and Shelley that are all about the mind of the individual. So, really, Browning’s title Dramatic Lyrics says it all. "My Last Duchess" is what would happen if Shakespeare’s Macbeth married Wordsworth’s "Tintern Abbey" and they had a baby. It’s a hybrid of a play and a poem – a "dramatic lyric."
As for meter, "My Last Duchess" uses the rhythm called "iambic pentameter." Iambic means that the rhythm is based on two-syllable units in which the first syllable is . . . oh, drat, your eyes are glazing over. Stay with us here. Okay, an iamb goes "da DUM," like that. Pentameter means that there are five ("penta") of those in a line. Listen: "There’s MY last DUCHess HANGing ON the WALL" – that’s iambic pentameter. Okay, okay, you could argue that "on" shouldn’t be stressed and so forth, but that’s the basic idea.
Why does this matter? Well, for one thing, some people like to claim that iambic pentameter is the most "natural" rhythm for the English language to fall into, and that we often speak in iambic pentameter without noticing. Nobody’s ever really been able to prove this, and probably nobody ever will, but it’s a persistent "myth" about meter, so you should know it’s out there. It also means that lines written in iambic pentameter feel conversational to us. If you listen to someone read "My Last Duchess" aloud (check out our "Links" section for some online audio recordings by contemporary poets and scholars), you might not even notice that it has a fancy meter, because it sounds more like normal speech than some other poetry does.
The other thing about iambic pentameter, like we said before, is that Shakespeare and other Elizabethan dramatists used it in their plays. Browning, a very highly educated writer, knew this, and his decision to use this meter in a poem that already feels sort of like a play is a direct allusion to the patterns of monologues (speeches made to others) and soliloquies (speeches made while alone) in drama. "My Last Duchess" is more of a monologue than a soliloquy, because there is a character listening to the Duke in the poem. He’s not speaking his thoughts aloud to himself while he’s alone, the way Hamlet does.
Of course, although the iambic rhythm makes us think of Elizabethan drama, the rhymed couplets (pairs of rhymed lines that occur together) of the poem keep tying the Duke’s speech into tidy packages, even though his thoughts and sentences are untidy. Both Shakespeare and the great Romantic poet William Wordsworth used iambic pentameter without rhyme, a form called blank verse. But Browning introduces couplets into the mix. We think you can probably guess why it might be more appropriate for the control-freak Duke of Ferrara to speak in harsh, structured, rhymed lines than in unrhymed ones.