Foraminifera are commonly used as index, marker of guide fossils for biostratigraphical zonation of sedimentary rock and sediments. This zonation permits the establishment of a relative age, a chronostratigraphy, for a sedimentary section. Micropaleontologists have established a wide-spanning net of biozones in space and time based on the first and last occurrences of selected species. From its foraminiferal content samples may be precisely placed into an according biozone.
Hundreds of scientific publications are available on biozonation with foraminifera but an overall and easy to use catalogue of index foraminifera is hard to get. With these pages we want to build such an easy to use catalogue of index foraminifera primarily for ourselves, but we share it with you.

According to Bellier et al. 2010, Page 19 and by personal remark of Robert Speijer species with biostratigraphic value should have the following characteristics:

As our compilation aims to be an easy to use tool for everyone we consider only easy recognition and common frequency in the designated area as the important criteria. We add also species with a long stratigraphic range as their first and last occurence dates are seen as useful time-marks. Applying extensive dispersion and facies-independancy would exclude benthic foraminifera. They though are much easier to recognize than planktonics. The obstacle of limited occurence of benthics shall be overcome by adding many.