The first two works, whose manuscripts had been prepared in Madrid the year before, were a grammar and a dictionary of Japanese. The third, prepared in 1631, while the larger works were being seen through the press, was a guide to the taking of confession written in both Latin and Japanese.[1] The grammar, drafted in Spanish, was published in Latin in 1632 under the title _Ars Grammaticae Iaponicae Linguae_. It is this work that is translated here. The dictionary, only at the last moment supplied with Latin glosses to supplement those in Spanish, was published in the same year with the title _Dictionarium sive Thesauri Linguae Iaponicae Compendium_.[2] Taken together these three works by Collado constitute the final extant efforts of those who studied the Japanese language first hand during the Christian Century.[3] Two other grammatical works must be mentioned here as central to the proper assessment of Collado's Grammar. They are both by the great Jesuit scholar, Father João Rodnguez (1561-1634);[4] the _Arte da Lingoa de Iapam_ (Nagasaki, 1604-8, hereafter the _Arte_), and the _Arte Breve da Lingoa Iapoa_ (Macao, 1620, hereafter _Arte Breve_). The first {2} is by any standards the greatest grammatical study of Japanese made during the Christian Century. It is further, as we shall see, the primary source for Collado's Grammar. The _Arte Breve_, on the other hand, is not directly related to Collado's work. Indeed it is clear that Rodriguez' 1620 Macao publication was unknown to Collado. Nevertheless, since the _Arte Breve_ is an abbreviated version of the _Arte_ with a purpose similar to the _Ars Grammaticae_, a comparison of these two books with respect to the way they systematize the material from the _Arte_ is included in this introduction to contribute some insight into the treatment of the Japanese language at the beginning of the Tokugawa Period. In presenting this translation two potential audiences are envisioned. The first, and more restricted, group is that having an interest in the history of the Japanese language. It is hoped that an English version of this work will make more readily available this significant material pertaining to the Japanese language as spoken in the early modern period. I use the word significant here to avoid granting excessive value to a work which derives such a large portion of its material and insight from Rodriguez' _Arte_.