The rapid adoption of smartphones and tablets as well as the widespread use of mobile applications has been fueling the growth of mobile commerce around the world. This paper quantifies the economic impact of tablets in ecommerce and m-commerce markets by examining its complementary and substitution effects with two other channels - PCs and smartphones. We use an archival data from the largest online and mobile commerce website in China (Taobao) and exploit a quasi-natural experiment to identify our results. Results show that the introduction of tablets enhanced the overall growth of ecommerce markets, with an annual impact of approximately US$3.04 billion. The tablet channel acts as a substitute for the PC channel and a complement for the smartphone channel. Further, our results highlight that consumers spend more when a tablet is simultaneously used with a PC, a smartphone, or both. The most revenue generating combination of simultaneous device usage is that of a smartphone and a tablet. Consumers also browse and purchase more distinct products when they adopt the tablet. We provide insights for retailers about how they can increase their sales volume and revenue in the emerging tablet economy.