Businesses everywhere still keep their books the way 1290s Florentine merchants did.
Double-entry bookkeeping records every transaction twice, as a debit in one account and an equal credit in another, so the books must always balance. The oldest surviving example is a Florentine firm's ledger from 1299. A friar who worked with Leonardo da Vinci published it for the world in 1494.
The core rule is that assets always equal liabilities plus equity. Every transaction touches at least two accounts in equal and opposite amounts. Buy 10,000 dollars of inventory on credit and both your inventory and what you owe rise by 10,000. Sell it for 15,000 in cash and cash goes up, inventory goes down, and the 5,000 difference shows up as profit in the owner's equity. Because debits must equal credits, a mismatch flags an error, or possibly fraud.
The earliest surviving books that follow the full modern system belong to Amatino Manucci, who worked for the Farolfi company, Florentine merchants based in Nîmes. Their ledger of 1299 to 1300 is fully double-entry. The method spread between Italian trading cities during the 14th century. It is often said that Giovanni di Bicci de' Medici introduced it to the Medici bank, but evidence for that is lacking.
The first known written description came from Benedetto Cotrugli, a merchant from Ragusa, now Dubrovnik, in 1458, but his treatise was not printed until 1573, and the printer garbled the section on bookkeeping. So the credit usually goes to Luca Pacioli, a Franciscan friar and collaborator of Leonardo da Vinci, whose mathematics textbook Summa de arithmetica, printed in Venice in 1494, laid out the method in detail. That is why he is often called the father of accounting.
In early modern Europe, the balanced ledger carried a sense of moral and even cosmic order, evoking both the scales of justice and the symmetry of God's creation. Today the same logic runs underneath spreadsheets and accounting software. The tools have changed completely; the idea that every entry has a matching opposite has not.
Source: Wikipedia — Double-entry bookkeeping · Text summarised from Wikipedia (CC BY-SA 4.0)
