6G is supposed to address the demands for consumption of mobile networking services in 2030 and beyond. These are characterized by a variety of diverse, often conflicting requirements, from technical ones such as extremely high data rates, an unprecedented scale of communicating devices, high coverage, low communicating latency, the flexibility of extension, etc., to non-technical ones such as enabling sustainable growth of the society as a whole, e.g., through the energy efficiency of deployed networks. On the one hand, 6G is expected to fulfill all these individual requirements, extending thus the limits set by the previous generations of mobile networks (e.g., ten times lower latencies, or a hundred times higher data rates than in 5G). On the other hand, 6G should also enable use cases characterized by combinations of these requirements never seen before, e.g., both extremely high data rates and extremely low communication latency). In this white paper, we give an overview of the key enabling technologies that constitute the pillars for the evolution toward 6G. They include terahertz frequencies (Section 1), 6G radio access (Section 2), next-generation MIMO (Section 3), integrated sensing and communication (Section 4), distributed and federated artificial intelligence (Section 5), intelligent user plane (Section 6) and flexible programmable infrastructures (Section 7). For each enabling technology, we first give the background on how and why the technology is relevant to 6G, backed up by a number of relevant use cases. After that, we describe the technology in detail, outline the key problems and difficulties, and give a comprehensive overview of the state of the art in that technology. 6G is, however, not limited to these seven technologies. They merely present our current understanding of the technological environment in which 6G is being born. Future versions of this white paper may include other relevant technologies too, as well as discuss how these technologies can be glued together in a coherent system.