Why do we need high-resolution observations of the Sun?

To make progress on major unsolved problems in solar physics (e.g., coronal heating, eruptive flare/CME initiation, solar wind initiation), we must observe on scales relevant to the underlying physical processes and their signatures. In this review I discuss the factors determining the structure of magnetic fields and plasmas in the Sun’s outer atmosphere, the key observable signatures of the relevant processes and properties, and the instrumental capabilities necessary to detect and measure these signatures. The primary emphasis is on state-of-the-art theoretical and numerical predictions, which often are the only means by which we can estimate the complex time-dependent evolution of the underlying physical mechanisms and their local and global effects on the corona.