Phase Plots of Complex Functions: a Journey in Illustration

We propose to visualize complex (meromorphic) functions $f$ by their phase $P_f:=f\mathrm{/}\mathrm{\mid }f\mathrm{\mid }$. Color–coding the points on the unit circle converts the function $P_f$ to an image (the phase plot of $f$), which represents the function directly on its domain. We discuss how special properties of $f$ are reflected by their phase plots and indicate several applications. In particular we reformulate a universality theorem for Riemann’s Zeta function in the language of phase plots.