This paper reviews Harry Grubert's contributions to the theory of consumption taxation, focusing on Grubert and Mackie (2000). Grubert and Mackie argue that financial services are not consumption and, therefore, need not be a direct part of the consumption tax base. Instead, financial services are like machines that transform resources over time or states of nature and, therefore, should be taxed like other machines in a consumption tax. The paper argues that Grubert and Mackie's theory is correct under the key assumption that the output of financial services (such as a higher level of consumption at a given time or state of nature) is taxed. If the output is not taxed, financial services should be taxed in the same way that durable goods are taxed.