Cephalopods are a diverse group of marine invertebrates with complex behaviors and ecological roles. Fossil cephalopods are abundant in strata across hundreds of millions of years of Earth’s history. Many cephalopods have carbonate (CaCO3) structures that grow through their lives and encode environmental conditions in their chemistry. I use multiple methods to measure and interpret geochemical changes of these structures in modern and fossil cephalopods. Much of my work relies on microanalytical techniques for measuring stable isotope ratios and slight variations in the elemental composition of these structures. Results from my work feed our understanding of modern cephalopods biology, extinct cephalopod behavior, paleoclimatology, and methods for the analysis of biogenic carbonate.