Among the earliest attempts of converting the Middle American Indians to Christianity was through the use of pictorial catechisms called Testerian manuscripts. The early Spanish Mendicant friars used the pictorial prayer books to teach the prayers of the Roman Catholic Church considered essential for conversion. The Testerian catechisms are named after Fray Jacobo de Testera, the Franciscan friar who is thought to have developed the hieroglyphic catechisms for the conversion process. The manuscripts combined Christian iconography and symbols from the pre-conquest native codices, and were drawn with small mnemonic and rebus figures representing a syllable, word or phrase of the Christian text The research undertaken in this study is the first comprehensive analysis of a group of manuscripts that were based on the pre-Columbian native codices and created for the religious education and conversion of the Indians of New Spain. Thirty-two documents are considered in this study. An analysis of style, content and form allowed us to define eleven types of Testerian catechisms represented by five groups and six individual examples. We have also determined that only nineteen of the extant manuscripts called Testerian catechisms are actual working catechisms, and that these were created over a time period of approximately three hundred years. The survival of the Testerian method into the nineteenth century reveals the prolonged success of the oldest teaching instruments of the New World, long after the native languages were transcribed into European letters, and three centuries following the merging of the two distinct and powerful New World and European cultures