This paper advocates for consistently defined units of account to measure the contributions of nature to human welfare. It argues that the term "ecosystem services" is too ad hoc to be of practical use in welfare accounting and proposes a definition rooted in economic principles. The goal is to ensure comparability with conventional goods and services in GDP and national accounts. The paper illustrates the definition with examples and argues that these units provide an architecture for environmental performance measurement by governments, conservancies, and environmental markets. It emphasizes the need for standardized units of account to improve environmental procurement and accounting, and to enable national-scale environmental welfare accounting and performance assessment. The paper discusses the challenges of defining ecosystem services, the importance of clear and precise definitions, and the need for standardized units to ensure consistency in measurement. It also highlights the importance of spatially explicit units and the need for proxies for services. The paper concludes that a clear, defensible, and consistent definition of ecosystem services is essential for effective environmental accounting and policy-making.This paper advocates for consistently defined units of account to measure the contributions of nature to human welfare. It argues that the term "ecosystem services" is too ad hoc to be of practical use in welfare accounting and proposes a definition rooted in economic principles. The goal is to ensure comparability with conventional goods and services in GDP and national accounts. The paper illustrates the definition with examples and argues that these units provide an architecture for environmental performance measurement by governments, conservancies, and environmental markets. It emphasizes the need for standardized units of account to improve environmental procurement and accounting, and to enable national-scale environmental welfare accounting and performance assessment. The paper discusses the challenges of defining ecosystem services, the importance of clear and precise definitions, and the need for standardized units to ensure consistency in measurement. It also highlights the importance of spatially explicit units and the need for proxies for services. The paper concludes that a clear, defensible, and consistent definition of ecosystem services is essential for effective environmental accounting and policy-making.