Double-entry book-keeping has been around for hundreds of years. The first evidence of its use dates back to the year 1211 in Florence, Italy. However, it was not until the year 1494 that the double-entry system was first codified by an Italian monk named Luca Paciola in a book called Summa de Arithmetica, Geometrica, Proportioni et Proportionalita (Everything about Arithmetic, Geometry and Proportion). Paciola recognised that every commercial transaction must be recorded in the books as both a debit and a credit, so that when the debits and credits are all added up, the totals must be the same. That is still the case today and underpins the concept of the Trial Balance. The basic principles of double-entry book-keeping have changed very little since Paciola wrote his book, although the methods used to apply them have of course changed out of all recognition.
An accounting system revolves around keeping ledgers to record every transaction, from the largest sale to the smallest petty cash expense. At the heart of any accounting system is the Cash Book. This records details of every financial transaction and allocates them to the various ledgers. The Sales Ledger, Purchase Ledger and Nominal Ledger are the main ones but there are many other sub-ledgers that also need to be maintained such as the fixed asset register, the stock records and various control accounts. The book-keeper must be able to reconcile these so that the balances match the amounts that actually exist.
A good book-keeper should possess the technical knowledge required to produce accounts up to trial balance stage. In addition, book-keepers must have sufficient knowledge of the business they are working for to understand the transactions themselves and how they should be recorded in the books. It is also important for there to be a proper audit trail so that you can drill down into the accounting records and see exactly what each account consists of and where the items originated.