E Ink (electrophoretic ink) is a specific proprietary type of electronic paper manufactured by E Ink Corporation, founded in 1997 based on research started at the MIT Media Lab. It is currently available commercially in grayscale and color and is commonly used in mobile devices such as e-readers and, to a lesser extent, mobile phones and watches.

On June 1, 2009, E Ink Corp. announced an agreement to be purchased by one of its primary business partners, Prime View Int'l Co. Ltd (元太科技工業), for US$215 million. It is predicted that the purchase by this Taiwanese company will put the production of the E-Ink EPD on a larger scale than before, as Prime View also owns BOE Hydis Technology Co. Ltd (京东方海帝士科技) and maintains a strategic partner relationship with Chi Mei Optoelectronics Corp., which is now Chi Mei Innolux Corp. (奇美電子), part of the Hon Hai-Foxconn Group (鴻海富士康集團). It is noteworthy that Foxconn is the sole ODM partner for Prime View's Netronix Inc. (振曜科技), the supplier of E-Ink-panel e-readers for rebranding (the end-user products may appear with any of several brands, e.g., Bookeen, COOL-ER, PocketBook, etc.).

Ink is a liquid or paste that contains pigments or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, or quill. Thicker inks, in paste form, are used extensively in letterpress and lithographic printing.

Ink can be a complex medium, composed of solvents, pigments, dyes, resins, lubricants, solubilizers, surfactants, particulate matter, fluorescers, and other materials. The components of inks serve many purposes; the ink’s carrier, colorants, and other additives control flow and thickness of the ink and its appearance when dry.

Ink formulas vary, but commonly involve four components:

Inks generally fall into four classes:

Pigment inks are used more frequently than dyes because they are more color-fast, but they are also more expensive, less consistent in color, and have less of a color range than dyes.

Pigments are solid, opaque particles suspended in ink to provide color. Pigment molecules typically link together in crystalline structures that are 0.1–2 µm in size and comprise 5–30 percent of the ink volume. Qualities such as hue, saturation, and lightness vary depending on the source and type of pigment.