Abstract: We present Fluid Inking, a generally applicable approach to augmenting the fluid medium of free-form inking with gestural commands. Our approach is characterized by four design criteria, including: 1) pen-based hardware impartiality: all interactions can be performed with a button-free stylus, the minimal input hardware requirement for inking, and the least common denominator device for pen-based systems ranging from PDAs to whiteboards; 2) performability: gestures use short sequences of simple and familiar inking interactions that require minimal targeting; 3) extensibility: gestures are a regular pattern of optional shortcuts for commands in an arbitrarily scalable menu system; and 4) discoverability: gesture shortcuts (analogous to modifier keys) are displayed in the interactive menu and are suggested with dynamic feedback during inking. This paper presents the Fluid Inking techniques in the unified context of a prototype notetaking application and emphasizes how post-fix terminal punctuation and prefix flicks can disambiguate gestures from regular inking. We also discuss how user feedback influenced the Fluid Inking design.