The proliferation of portable electronic devices has caused increased interest in new display technologies that overcome the many limitations in traditional flat panel displays. In particular, most current display technologies, particularly those based on fluids, require one or more sheets of glass in the display construction. One strategy for making fluid-based display technologies compatible with film substrates is to create a dispersion of a fluid in a polymer matrix. Microencapsulated electrophoretic displays@footnote 1@ ("electronic ink") offer a unique and interesting set of properties: high reflectivity and contrast, a paperlike appearance, low power consumption, and compatibility with flexible substrates. In electronic ink displays, microcapsules serve to contain a colored, nonaqueous fluid containing electrophoretically-mobile particles. An electric field is used to move particles to either the front or back of the display, so that a viewer either sees the particles or the colored oil. Depending on the surface chemistry of the colloid and polymer, the particles can remain in place long after the electric field is removed. This property gives the display image an inherent persistence of the without further power consumption. Here, I will describe the optical and electrical characteristics of these microencapsulated display materials based on rutile titanium dioxide colloidal particles. Electronic ink devices are also highly compatible with microelectronic circuits, either based on traditional silicon devices or on novel semiconducting organic materials, and I will also discuss recent progress in this integration. @FootnoteText@ @footnote 1@B. Comiskey, J.D. Albert, H. Yoshizawa, J. Jacobson, Nature, 394, 253 (1998).