One of my most vivid memories from college is my Struct I professor teaching us that civil engineering is an empirical field. He wasn’t just defining what empirical meant, he was also teaching us we need to ready our minds for change. This instruction came at a fortuitous time. This was 1997 and three years prior to that the Northridge earthquake had rocked Los Angeles and was about to change the way structural engineers look at seismic design and detailing forever. Beginning with the changes codified in the 1997 UBC, the standard of practice for seismic design today has evolved to become radically different from what was followed prior to Northridge. In this article the change I would like to help us all understand is multi-period seismic in ASCE 7-22 — where it came from, what’s “multi-” about it, and how it will affect what you do in your own designs.