A growing chorus of voices critical of contemporary architectural practice is pointing to the excessive use of glass in building skins as a primary culprit in the carbon emissions plaguing earth’s atmosphere. New York City Mayor DeBlasio raised the pitch most recently threatening a ban on “…the glass and steel skyscrapers that have contributed so much to global warming.” Building scientists have pointed to the fallibility of the tall glass curtainwall building type. The glass industry points to the significant benefits of glass in daylighting and connection to the outdoor environment. Architects want maximum transparency and minimal sight lines. Occupants want floor-to-ceiling glass. This demand continues to produce buildings with significantly compromised performance, a trend on a collision course with escalating code requirements driven by the pursuit of reduced carbon emissions in the building sector. Balancing the benefits and liabilities of glass in the building skin is the most challenging factor in building design and performance today. Academic and industry thought leaders peel back the layers of the glass onion.