In the Principia, Book One, Section I, Newton outlines his method of prime and ultimate ratios, which is essentially a theory of limits.
Isaac Newton's main work is Philosophia Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), or short Principia, which is by some also thought to be the greatest mathematical work of all times.
During Newton's lifetime this book was published in three authorised editions: in London 1687, Cambridge 1713, and again London 1726. The two unauthorised versions were both published in Amsterdam, one in 1714, the other in 1723. The Latin text available here is taken from the 3rd edition of the Principia, published in 1726. The English translation was made by Andrew Motte and published in 1729.