This is the first in a series of four continuing professional development articles that explain some of the principles of economic assessment and describe the most commonly cited approaches. The series aims to enable readers to critically examine economic assessments in the context of nurse-led service innovation. It introduces a tried-and-tested methodology, with associated tools and templates, used to conduct economic assessments in nursing. In this article, the principles of economic assessment are introduced and two case studies of nurse-led innovation are used to illustrate how they are applied in practice.