Costumes Are Mandatory is a studio album by American jazz pianist Ethan Iverson recorded with saxophonist Lee Konitz, bassist Larry Grenadier, and drummer Jorge Rossy.

"[7] Thom Jurek of AllMusic added, "Costumes Are Mandatory is anything but a conventional recording: these players communicate, inquire, and argue with one another as much as they do Tristano and seem to delight in the process, which is a reward for any jazz listener.

"[4] In his review for JazzTimes, Lloyd Sachs stated, "Far from your classic session combining a young cutting-edge stalwart and revered master, Costumes Are Mandatory is a quirky assemblage of odds and ends.

Framed as an homage to Lennie Tristano, it sometimes teams pianist and project instigator Ethan Iverson and alto great (and former Tristanian) Lee Konitz and sometimes features piano pieces that possibly were recorded to fill out the album.

[8] Writing for HuffPost contributor Ralph A. Miriello observed, "Costumes Are Mandatory is a wonderful body of music that more than makes up for some of its rough spots by offering moments of unvarnished beauty from a marvelously supple group of musicians and magical playing by Mr. Konitz, a living legend of his craft"[9] Chris Smith of Winnipeg Free Press commented, "Grenadier's full-bodied bass and Konitz's wandering alto are a superb combination.