Balance of Payments
A precise encyclopedia entry explaining the concept of 'Balance of Payment'.
Another brief article on 'Balance of Payment' from an authoritative source.
Downloadable time series data including, "Quarterly and annual estimates of transactions with foreigners... trade in goods and services, receipts and payments of income, capital-account transactions, and transactions in financial assets and liabilities."
IMF disseminates a wide range of information in the area of balance of payments and international investment position (IIP) statistics.