The Grolier Codex (sometimes referred to as the Saenz Codex) is a pre-Columbian Maya document of disputed authenticity. It first appeared in a private collection in the 20th century and was displayed at the Grolier Club in New York, hence its name. The codex consists of a looted fragment of a Maya book, containing almanacs of Venus represented in a simplistic fashion. The Grolier Codex would be only the fourth surviving pre-Columbian Maya book if genuine. The codex is said to have been recovered from a cave in the Mexican state of Chiapas in the 1960s, together with a mosaic mask and some blank pages of pre-Columbian fig-bark paper. It was displayed at the Grolier Club in 1971, and is now held in Mexico City. In 1973, Michael D. Coe (Wikipedia page [1]) published a facsimile of the codex in The Maya Scribe and his World, produced by the Grolier Club. The codex contains a Venus almanac that, in structure, is closely related to the Venus almanac contained in the Dresden Codex.
More information - including details of its discovery and investigations into its authenticity - on the Wikipedia page [2].