Marketing has enjoyed unparalleled transformation in terms of its effectiveness and ability to delivery measurable return on investment due to the digital revolution. The spread of blockchain technology has led to suggestions that it may have significant marketing applications. Though blockchain is indeed an amazing technology with significant applications, this paper argues that its usefulness in many traditional marketing applications may be limited. The reasons why throw important light on the interactions between blockchain technologies, data and privacy. Blockchain, by its nature, may lead to substantial privacy harms when used indiscriminately for marketing purposes.11This research is based on insights from two previously published papers - Tucker and Catalini (2018) and Marthews and Tucker (2019)