Global initiative and research on 6G have grown rapidly since 2018. The rollout of 5G is driving our life, industry, and society toward a connected and smart world. 6G is envisioned not only as a successor but also as a disruptor of 5G. It will further enhance the capability, energy and spectral efficiencies, and quality of experience and will also bring a fully intelligent, secure, and sustainable world. In this chapter, we will provide our vision on what 6G will be as well as its potential applications and main challenges for its successful implementation. We will start by presenting a brief overview of 5G technologies and the inherent standardization process, along with some discussions on the capability gaps toward 2030. A preliminary discussion on 6G objectives, technologies, and roadmap will be first provided. After this introductory part, this chapter will discuss more in-depth our vision toward 6G. In particular, the enabling technologies and challenges for guaranteeing (i) all things sensed and connected, (ii) all things intelligent, (iii) all things sustainable, and (iv) all things secured will be discussed. The chapter will be concluded by summarizing the main technologies toward 6G.