The EPSI file extension is used by Encapsulated PostScript Interchange Files. The format is based on the PostScript dynamically typed concatenative programming language developed by Adobe Systems and used mostly within desktop publishing. PostScript files are self-contained documents that follow the DSC (Document Structuring Conventions) set of standards.

The Encapsulated PostScript format is mostly used for saving documents which can contain text, raster graphics, vector graphics and a set of page formatting properties. The default extensions for these files are EPS and EPSF. EPSI files are used to display preview images for Encapsulated PostScript documents.

Three other formats may also be used for creating preview images but the EPSI format is the only device independent one able to provide consistent bitmap data across all systems. The image data stored in EPSI files is encoded using only 7-bit ASCII characters and requires no decoding or decompression.