The IoT extends the idea of interconnecting computers to a plethora of different devices, collectively referred to as smart devices. These are physical items, that is, "things", such as wearable devices, home appliances, and vehicles, enriched with computational and networking capabilities. Due to the huge set of devices involved, and therefore its pervasiveness, IoT is a great platform to leverage for building new applications and services or extending existing ones. In this regard, expanding online advertising into the IoT realm is an under-investigated yet promising research direction, especially considering that the traditional Internet advertising market is already worth hundreds of billions of dollars. In this article, we first propose the architecture of an IoT advertising platform inspired by the well known business ecosystem, which the traditional Internet advertising is based on. Additionally, we discuss the key challenges to implement such a platform, with a special focus on issues related to architecture, advertisement content delivery, security, and privacy of the users.