As infrared spectroscopy (IR) is frequently used in undergraduate organic chemistry courses, an inductive introduction to IR spectroscopy that uses index cards printed with spectra, structures, and chemical names is described. Groups of students are given an alphabetized deck of these "IR cards" to sort into functional groups. The students then determine each functional group's infrared "signature" by comparing several spectra containing a specific functional group. Response to the IR cards was favorable, and students were more proficient in subsequent laboratories that used IR spectroscopy. This experiment is suitable for use in a one-semester or full-year organic course. (Contains 4 tables and 1 figure.)