A text file filter is a program that converts one text file into another on the basis of a set of rules. For statistical applications, a text file filter can convert data embedded in a complicated text file so that Stata can read and analyze it. A text file filter can also automate the production of more user-friendly output from long Stata log files. The file command lets you use text file filters in Stata. This article reviews some key programming points for successful implementation of such filters.