Institutes of the Christian Religion

Institutes of the Christian Religion is John Calvin's seminal
work on Protestant systematic theology. Highly influential in the Western world
and still widely read by theological students today, it was published in Latin
in 1536 and in his native French in 1541, with the definitive editions appearing
in 1559 (Latin) and in 1560 (French).

The book was written as an introductory textbook on the Protestant faith for
those with some learning already and covered a broad range of theological topics
from the doctrines of church and sacraments to justification by faith alone and
Christian liberty, and it vigorously attacked the teachings of those Calvin
considered unorthodox, particularly Roman Catholicism to which Calvin says he
had been "strongly devoted" before his conversion to Protestantism. The
over-arching theme of the book – and Calvin's greatest theological legacy – is
the idea of God's total sovereignty, particularly in salvation and election. The
Institutes are a primary reference for the system of doctrine adopted by
the Reformed churches, usually called Calvinism.

- Excerpted from the Wikipedia