Treasury Bills, Commercial Paper, Corporate Bonds, Certificate of Deposits and Repurchase Agreements. Collectively are referred to as Money Market Instruments.Money market instruments are short term debt obligations generally regarded as low risk, low to medium return investment for the holder. They are essentially IOUs issued by governments, financial institutions and large corporations. These instruments are very liquid and considered extraordinarily safe. Because they are extremely conservative, money market securities offer significantly lower risks than most other securities. They have maturities ranging from one day to one year.
Treasury billsTreasury bills are issued by the Central banks such as the Bank of England or government treasury departments. The Treasury sells bills at regularly scheduled auctions to refinance government projects and obligations.  It also helps to finance current government deficits.Commercial PaperCommercial Paper is short-term loan that is issued by a corporation use for financing accounts receivable and inventories. Commercial Papers have higher denominations as compared to the Treasury Bills and the Certificate of Deposit. The maturity period of Commercial Papers is a maximum of 9 months. They are very safe since the financial situation of the corporation can be anticipated over a few months.

Corporate Bonds

A corporate bond is an IOU issued by a public company, such as BT, ICI or Marks & Spencer. When you invest in a corporate bond, you are lending money to the company. In return you will receive interest at a fixed rate and the promise that your capital will be repaid at a certain date in the future.
Certificate of Deposit
A certificate of deposit (CD) is a time deposit with a bank. CDs are generally issued by commercial banks but they can be bought through brokerages. They bear a specific maturity date (from three months to five years), a specified interest rate, and can be issued in any denomination, much like bonds. CDs offer a slightly higher yield than Treasury Bills because of the slightly higher risk for a bank but, overall, the likelihood that a large bank will go broke is pretty slim. (Northern Rock Plc being the exception of course).
Repurchase Agreements
The Repo or the repurchase agreement is used by the government security holder when he sells the security to a lender and promises to repurchase from him overnight. Hence the Repos have terms raging from 1 night to 30 days. They are very safe due to government backing. Due to this short turnaround time, these agreements are the most liquid of all money market investments, they are very similar to bank deposit accounts, and many corporations arrange for their banks to transfer excess cash to such funds automatically.
It is however important to note that Although securities purchased on the money market carry less risk than long-term debt, they are still not entirely risk free. After all, as we all know banks do sometimes fail, and the fortunes of companies can change rather rapidly. But it has to be said that the range of possible outcomes is less for short-term investments than for conventional equity and fixed income investments.

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