# Books

> An entity's book for the general ledger: the currency it keeps, the date it is closed through, and its statements.

A book is one legal entity's set of books for the general ledger, such as its US GAAP books. Every
invoice, payment, and [journal entry](/docs/apps/finance/journal-entries) posts in a book.

## How it works

A book keeps its balances in one currency. An entity has one **Primary** book per ledger, and
invoices and payments post to it. It can keep **Secondary** books beside it, such as IFRS. A book's
kind and currency do not change once you create it.

### Close a period

To close a period, set the book's **Lock date**. Nothing dated on or before that date can post.
Move the date forward as you close each period.

### Read the statements

Open a book and go to **Statements** to see its **Balance sheet**, **Income statement**, and
**Trial balance**, as of a date you choose. The income statement covers the year to that date.
Every amount is in the book's currency.

<RecordReference type="finance.book" />

## Next steps

<Cards>
  <Card title="Ledger accounts" href="/docs/apps/finance/accounts" icon="list">
    Set up your chart of accounts.
  </Card>
  <Card
    title="Customer accounts"
    href="/docs/apps/finance/customer-accounts"
    icon="users"
  >
    Set up whom an entity bills.
  </Card>
</Cards>