*Karaṇapaddhati **of Putumana Somayājī* is an important text of the Kerala School of astronomy and mathematics, probably composed in the 16th century. In the Indian astronomical tradition, the

*karaṇa *texts are essentially computational manuals and they often display a high level of ingenuity in coming up with simplified algorithms for computing planetary longitudes and other related quantities.

*Karaṇapaddhati*, however, is not a

*karaṇa *text. Rather, it discusses the

*paddhati** *or the rationale for arriving at suitable algorithms that are needed while preparing a

*karaṇa *text for a given epoch. Thus the work is addressed not to the almanac maker but to the manual maker.

*Karaṇapaddhati *presents the theoretical basis for the *vākya *system, where the true longitudes of the planet are calculated directly by making use of certain auxiliary notions such as the *khaṇḍa*, *maṇḍala *and *dhruva** *along with tabulated values of changes in the true longitude over certain regular intervals which are expressed in the form *vākyas *or mnemonic phrases. The text also discusses the method of *vallyupasaṃhāra *which is essentially a technique of continued fraction expansion for obtaining optimal approximations to the rates of motion of planets and their anomalies, involving ratios of smaller numbers. It also presents a new fast convergent series for π which is not mentioned in the earlier works of the Kerala School. As this is a unique text presenting the rationale behind the *vākya *system and the computational procedures used in the *karaṇa *texts, it would serve as a useful companion for all those interested in the history of astronomy. The authors have provided a translation of the text followed by detailed notes which explain all the computational procedures, along with their rationale, by means of diagrams and equations.