Jerome Kern wrote “All the Things You Are” in 1939 for the musical Very Warm for May, with lyrics by Oscar Hammerstein II. The show flopped. The song didn’t. Jazz musicians fell in love with its constantly shifting key centers, and today it’s arguably the most-played standard at jam sessions worldwide.
The form is 36 bars, laid out A A B A, with the last A stretched to 12 bars. It’s written in Ab major, but it barely stays there. The first A runs down the cycle of fourths (Fm7, Bbm7, Eb7, Abmaj7, Dbmaj7) and then lands in C major. The second A repeats the idea a fourth lower, landing in G. The bridge moves to G and then pivots to E major before a half-step slide sets up the return. The last A starts like the first, then detours through Dbm7 (the minor iv) before closing in Ab.
That’s the improvisation lesson: you’re constantly moving between tonal centers, so you need to hear where each ii-V is going. Practice by labeling every key center on your lead sheet, then improvise using only the scale of each center. Next, find the common tones that connect them. For example, the move from Abmaj7 to Dbmaj7 shares C and F, so you can hold those notes and let the harmony move underneath you. The bridge into E major is where most players get lost, so loop those eight bars on their own.
One more tip: the famous intro and ending vamp many bands use comes from the Charlie Parker and Dizzy Gillespie era, built on a repeated chromatic figure. Learn it, because the band will expect it at most jam sessions.
Learn it in Ab first, then in the other common keys horn players use. Charlie Parker, Bill Evans and Keith Jarrett all recorded famous versions worth transcribing. Read more about the composer on Jerome Kern’s Wikipedia page, and browse more standards with key-center breakdowns at Minedit.