This chapter provides a basic understanding of trends as a theoretical construct to facilitate dealing with the future. Trends can be defined at different levels, from individual technology trends to overarching megatrends. In this context, their development is driven by the complex interplay with their environment. Some mechanisms can be abstracted by the diffusion model by Rogers or the Gartner Hype Cycle. However, the concrete course of trends is complex and cannot be predicted in detail.