Purpose – For centuries, gratitude has represented an integral component of social relationships, yet it remains relatively overlooked by marketing scholars in the study of commercial relationships. The purpose of this paper is to demonstrate how gratitude helps to build, maintain and transform commercial relationships and to suggest noteworthy areas of investigation for those researchers seeking to help companies understand the role of gratitude in relationship marketing. Design/methodology/approach – Gratitude's role in relational exchange is explored by a review of relevant literature and two qualitative studies. Questions developed from the literature and exploratory interviews are then investigated in a main study through in-depth interviews with buyers and sellers of goods and services in both B2B and B2C contexts, leading to a grounded theoretical foundation. Generalizations and directions for future research are presented. Findings – Gratitude is a fundamental component of buyer-seller relationships and is critical for advancing relationship marketing theory and practice. Gratitude's changing role as relationship stages advance is described. Research limitations/implications – The research is of an exploratory nature. Confirmation of the generalizations by other studies is suggested. This research is largely consistent with that from a markets-as-networks perspective and moves relationship marketing research toward a more extended view. Practical implications – Gratitude should be included along with other relational mediators in discussions and investigations of relationship success, and practiced by those that seek to build, develop and enhance their buyer-seller relationships. Originality/value – This paper provides a much needed exploration of a new and important topic in relationship marketing and a call for gratitude to be studied and implemented in a variety of relational exchange contexts. Specifically, it is the first to address the importance of gratitude to both buyers and sellers in B2B and B2C goods and services markets. It also is the first to document the changing role of gratitude through relationship stages.