The interfacial electric field profile is typically defined as the negative gradient of a spatially varying electrostatic potential landscape. In solution-phase systems, this seemingly straightforward relationship can lead to confusion because there are multiple related yet non-equivalent ways that the electrostatic potential can be defined. Although these different definitions are thermodynamically consistent, they predict very different interfacial field profiles. These profiles are consequential because they motivate our molecular-level understanding of interfacial chemical processes.