If green accounting is to be taken seriously, the accounts must not be only concerned with the ways in which services are weighted (the missing prices problem) but also with the definition of services themselves. Moreover, it is desirable to define ecosystem service units in a way that is methodologically and economically consistent with the definition of goods and services used in the conventional income accounts. In a nutshell, the national income accounts add up things bought and sold in the economy, weighted by their prices, in order to arrive at an aggregate, such as the nation’s gross domestic product.