Credit bureaus are companies that compile information about your financial history and report it to potential lenders who are trying to determine whether or not to issue you a loan.
Banks that have issued you a mortgage or other type of loan will inform credit card companies whether or not you made your payments on time.
Credit Card Companies
Credit card companies report your credit limit, balance and whether your payments are current.
Utilities like gas, electric and water will report whether or not you are current with your payments.
Installment Loan Issuers
Companies that have issued you an installment loan such as monthly payments for a new television will report your payments or lack thereof.
If you have had a collections agency used against you to collect money you owe, it will report whether or not you paid your debts.